Skin & Subcutaneous Tissue

Basal cell carcinoma: recognition and management

Clinical Overview and When to Suspect Basal Cell Carcinoma

— Cumulative and intermittent intense UV exposure (especially UVB); childhood sunburns are strongly contributory

— Fair skin (Fitzpatrick I–II), blue/green eyes, red/blond hair, freckling, inability to tan

— Age >50, male sex (though gap narrowing), outdoor occupations, tanning bed use

— Immunosuppression: solid organ transplant recipients have 5–10× risk; HIV, chronic immunosuppressants, CLL

— Prior ionizing radiation (e.g., childhood scalp irradiation, radiotherapy fields)

— Chronic arsenic exposure (well water, traditional remedies)

— Genetic syndromes: Gorlin (nevoid BCC) syndrome (PTCH1 mutation, multiple BCCs <20 yo, jaw keratocysts, palmar pits, calcified falx), xeroderma pigmentosum, Bazex-Dupré-Christol, Rombo

— A non-healing, slowly enlarging papule or plaque on sun-exposed skin (head/neck 80%, especially nose, ears, periocular, lip)

— Lesion that bleeds with minor trauma, crusts, then re-bleeds in a "comes and goes but never fully heals" pattern

— Pearly translucent papule with telangiectasias and rolled borders

— A new "pimple" in an older adult that has persisted >1 month

Basal cell carcinoma (BCC) is the most common human malignancy, arising from pluripotent cells of the basal layer of the epidermis and follicular structures.

Epidemiology and risk drivers:

When to suspect in a family medicine visit:

Board pearl: BCC almost never metastasizes (<0.1%) but causes substantial local destruction—the "rodent ulcer" can invade cartilage, bone, and orbit if neglected. Mortality is low; morbidity from disfigurement is high.

Step 3 management: Any persistent, non-healing skin lesion in a sun-exposed area of an older or fair-skinned adult warrants full-body skin examination and biopsy of the suspicious lesion—do not "watch and wait" beyond 4–6 weeks.

Presentation Patterns and Key History

— Duration: BCCs grow slowly over months to years; rapid growth (weeks) suggests SCC or keratoacanthoma

— Symptoms: usually asymptomatic; may bleed, crust, itch mildly; pain or numbness suggests perineural invasion (red flag)

— Prior skin cancers (personal/family), prior cryotherapy or "frozen spots," prior Mohs surgery

— Sun exposure pattern, tanning bed use, sunscreen habits, outdoor occupation/hobbies

— Immunosuppression history: transplant, HIV, biologics, chemotherapy

— Radiation exposure, arsenic, smoking

— Nodular BCC (50–80%): pearly, translucent, dome-shaped papule with overlying arborizing telangiectasias and rolled border; central ulceration ("rodent ulcer") common; favors face

— Superficial BCC: erythematous, scaly, well-demarcated patch with fine thread-like pearly border; favors trunk/extremities; mimics eczema or psoriasis

— Morpheaform/sclerosing/infiltrative BCC: ill-defined, white-yellow scar-like indurated plaque; subclinical extension typical, high recurrence risk

— Pigmented BCC: nodular variant with brown/black pigment; mimics melanoma; more common in darker skin types

— Basosquamous: hybrid features with BCC and SCC; behaves more aggressively, higher metastatic risk

Key history elements to elicit:

Clinical subtypes—high-yield recognition:

Key distinction: A shiny, pearly, telangiectatic quality on dermatoscopy or stretch examination strongly favors BCC over benign intradermal nevus or sebaceous hyperplasia—sebaceous hyperplasia is yellow with a central dell and lacks arborizing vessels.

Board pearl: A superficial BCC on the trunk is the classic "treatment-resistant eczema patch" that didn't respond to topical steroids for months—biopsy any unilateral, persistent, sharply demarcated scaly plaque.

Step 3 management: Document lesion size, location, borders, photographs, and prior treatments before biopsy—this drives later staging and Mohs eligibility decisions.

Physical Exam Findings and Full-Skin Assessment

— Inspect under bright, tangential lighting; stretch the skin to reveal pearly translucency and telangiectasias

— Dermatoscopy findings: arborizing ("tree-branch") vessels, blue-gray ovoid nests, leaf-like areas, spoke-wheel structures, shiny white streaks, ulceration

— Palpate for induration, fixation to deeper structures, and lesion depth

— Measure greatest diameter in mm; photograph with a scale marker

— "Mask areas" of face: central face, eyelids, eyebrows, periorbital, nose, lips (cutaneous and vermilion), chin, mandible, preauricular/postauricular, temple, ear

— Genitalia, hands, feet, ankles, nipples

— Lesions in these zones qualify as high-risk regardless of size and typically require Mohs

— Palpate regional lymph nodes (rare in BCC but mandatory in basosquamous or large neglected lesions)

— Cranial nerve exam if perineural symptoms (facial numbness, twitching, diplopia)

— Full-body skin exam (FBSE): scalp (part hair), retroauricular, conjunctivae, oral mucosa, interdigital, soles, genitalia, gluteal cleft

— Count and map all suspicious lesions; many patients have multiple synchronous keratinocyte carcinomas and actinic keratoses

Lesion-level examination:

Anatomic risk zones (NCCN "H-zone" = high risk):

Regional and systemic exam:

Board pearl: Patients with one BCC have ~40–50% risk of another within 5 years—a single lesion mandates a complete skin exam and a long-term surveillance plan, not just excision of the index lesion.

Step 3 management: Use the ABCDE for melanoma to screen pigmented lesions during the FBSE; do not anchor on the chief-complaint lesion. Document a baseline body map for high-risk patients (transplant, Gorlin, prior NMSC).

Key distinction: Hemodynamic instability is not part of BCC; if a patient presents with bleeding from a facial lesion causing hemodynamic compromise, suspect erosion into a named vessel (angular, superficial temporal) and pursue urgent ENT/surgical evaluation.

Diagnostic Workup — Biopsy as the Initial Confirmatory Step

— Shave (tangential) biopsy: preferred for most suspected BCCs; samples epidermis and superficial dermis; quick, low-cost, good cosmesis

— Punch biopsy (3–4 mm): useful for morpheaform/infiltrative lesions where deeper sampling is needed, or pigmented lesions where melanoma cannot be excluded

— Excisional biopsy: small lesions on non-cosmetic sites; rarely needed pre-Mohs

— Avoid curettage alone as a diagnostic specimen—architecture is lost

— Anesthetize with 1% lidocaine + epinephrine (safe on nose, ears, digits in standard concentrations)

— Achieve hemostasis with aluminum chloride or electrocautery

— Submit in 10% formalin; specify clinical impression and anatomic site on the requisition (improves pathology accuracy)

— No CBC, CMP, or tumor markers needed

— Pre-procedure labs only if patient has bleeding disorder, is on anticoagulation requiring management, or has comorbidities

— Review anticoagulants/antiplatelets: generally continue aspirin, clopidogrel, warfarin (if INR therapeutic), and DOACs through small skin biopsies and most Mohs procedures—bleeding risk lower than thromboembolic risk

Skin biopsy is the diagnostic gold standard—no labs or imaging substitute for tissue.

Biopsy technique selection:

Practical biopsy tips:

Laboratory studies—generally not required for routine BCC:

Board pearl: Do not stop medically necessary anticoagulation for routine skin biopsy or Mohs—this is a frequently tested patient safety point. Cessation has caused strokes; intraoperative bleeding is manageable.

CCS pearl: Order "skin biopsy, shave" followed by "pathology consultation"; advance the clock 5–7 days for results before ordering definitive treatment.

Step 3 management: If biopsy returns "BCC, subtype not specified," call the pathologist or request re-cut with subtyping—subtype (nodular vs. infiltrative vs. morpheaform) drives whether standard excision or Mohs is appropriate.

Diagnostic Workup — Advanced and Staging Studies for Aggressive Disease

— Perineural symptoms: facial numbness, paresthesia, weakness, diplopia → MRI with contrast of face/skull base to assess perineural spread along V1, V2, V3, or facial nerve

— Bone invasion suspected (fixed lesion over bone, deep ulceration) → CT with contrast of affected region

— Orbital involvement (medial canthus lesions, lid retraction, proptosis) → MRI orbits + ophthalmology referral

— Suspected nodal or distant metastasis (basosquamous, neglected giant BCC, immunosuppressed) → CT neck/chest or PET-CT

— Histologic subtype (nodular, superficial, micronodular, infiltrative, morpheaform, basosquamous)

— Depth of invasion, perineural invasion (PNI), lymphovascular invasion

— Margin status if excisional specimen

— T1: ≤2 cm; T2: >2–4 cm; T3: >4 cm or deep invasion (beyond subcutaneous fat, perineural, or bone erosion); T4: skull base/axial skeleton invasion

— N and M staging mirrors other cutaneous carcinomas; clinical staging suffices for most—imaging only if signs of regional/distant disease

— Location in H-zone, size ≥10 mm on cheek/forehead/scalp/neck or ≥20 mm on trunk/extremities

— Poorly defined borders, recurrent lesion, immunosuppression, prior radiation site

— Aggressive subtype (infiltrative, micronodular, morpheaform, basosquamous), perineural involvement

Most BCCs require no imaging. Reserve advanced workup for high-risk features:

Pathology report elements that drive staging:

Staging—AJCC 8th edition for cutaneous BCC of head/neck (separate from trunk/extremity):

NCCN high-risk features (any one upgrades management):

Board pearl: Perineural invasion on pathology mandates MRI even if the patient is asymptomatic—silent spread along cranial nerves can extend to the skull base and changes treatment to include adjuvant radiation.

Step 3 management: Refer to Mohs surgeon and multidisciplinary tumor board for any T3/T4 lesion, PNI-positive disease, or recurrent BCC in cosmetically sensitive areas before definitive therapy.

Risk Stratification and First-Line Management Logic

— Trunk/extremity <20 mm OR cheek/forehead/scalp/neck/pretibial <10 mm

— Well-defined borders, primary (not recurrent), no immunosuppression, no prior RT at site

— Nodular or superficial subtype only, no perineural involvement

— H-zone location, size thresholds above exceeded, poorly defined borders

— Recurrent, immunosuppressed host, site of prior radiation

— Aggressive histology, perineural invasion, neurologic symptoms

— Low-risk, superficial BCC: topical therapy (5-FU, imiquimod), cryotherapy, electrodessication and curettage (ED&C) off hair-bearing areas, or standard excision with 4 mm margins

— Low-risk, nodular BCC: standard excision with 4 mm margins (cure ~95%) or ED&C in select sites

— High-risk BCC: Mohs micrographic surgery is preferred; alternative is wide excision with intraoperative or comprehensive margin assessment (cure 97–99% with Mohs)

— Inoperable/locally advanced or metastatic: hedgehog pathway inhibitors (vismodegib, sonidegib); consider radiation therapy

— Patients who decline or cannot tolerate surgery (elderly, poor surgical candidates)

— Adjuvant after surgery for PNI, positive/close margins, or large tumors

— Avoid in <60 yo when possible (secondary malignancy risk) and in genetic syndromes (Gorlin—radiation induces more BCCs)

Stratify every BCC into low-risk vs high-risk before choosing therapy (NCCN framework).

Low-risk BCC (all criteria met):

High-risk BCC (any one):

Treatment matrix:

Radiation therapy indications:

Board pearl: Gorlin syndrome patients should not receive radiotherapy—it triggers explosive BCC formation in the radiation field. Surgery and hedgehog inhibitors are preferred.

Step 3 management: Document a shared decision-making conversation covering cure rate, cosmesis, anesthesia, recovery, and cost for every treatment recommendation—Step 3 frequently tests appropriateness of modality selection.

Key distinction: Mohs is tissue-sparing with 100% margin assessment; standard excision examines only 1–2% of the margin (breadloafing)—this drives the Mohs preference in cosmetically/functionally critical areas.

Pharmacotherapy — Topical and Systemic Agents

— Indication: superficial BCC on trunk/extremities, low-risk; not for nodular or facial lesions

— Regimen: apply BID × 3–6 weeks; expect erythema, erosion, crusting (signals efficacy)

— Counsel: avoid sun exposure; use gloves to apply; avoid mucous membranes

— Cure rates ~70–80%—lower than surgery, so reserve for appropriate cases

— Indication: superficial BCC ≤2 cm on trunk/extremities/neck; immunomodulator (TLR-7 agonist)

— Regimen: 5 nights/week × 6 weeks

— Side effects: brisk inflammation, flu-like symptoms, pigmentary changes

— Avoid in pregnancy (category C), immunocompromised hosts, and on the face/genitalia in most cases

— Vismodegib 150 mg PO daily: SMO inhibitor; objective response ~30–60%

— Sonidegib 200 mg PO daily: alternative SMO inhibitor

— Adverse effects: muscle spasms, alopecia, dysgeusia (taste loss), weight loss, fatigue, amenorrhea, hepatotoxicity

— Teratogenic—category X; require contraception (women: during and 24 months after vismodegib, 20 months after sonidegib; men: condoms during and 3 months after); no blood donation during and 24 months after

— FDA-approved for locally advanced or metastatic BCC after hedgehog inhibitor failure or intolerance

— Immune-related adverse events: pneumonitis, colitis, hepatitis, endocrinopathies—monitor TSH, LFTs, glucose

— Wound care after topical therapy: petrolatum, non-stick dressings

— Sun protection during and after treatment (SPF 30+, broad-spectrum)

Topical 5-fluorouracil (5-FU) 5% cream:

Topical imiquimod 5% cream:

Hedgehog pathway inhibitors—for locally advanced or metastatic BCC, or patients ineligible for surgery/radiation:

Cemiplimab (anti-PD-1):

Adjunctive supportive care:

Board pearl: Vismodegib's signature triad—muscle cramps, alopecia, and dysgeusia—appears in nearly all patients and is a common reason for discontinuation; counsel upfront and consider planned drug holidays.

Step 3 management: Before starting a hedgehog inhibitor, confirm pregnancy status (β-hCG), document contraception, baseline LFTs and CK, and arrange dermatology/oncology co-management.

Procedural Management — Excision, Mohs, ED&C, and Cryotherapy

— 4 mm clinical margins for low-risk BCC; depth to mid-subcutaneous fat

— Send specimen for permanent section with margin assessment; re-excise if positive

— Closure: primary, flap, or graft depending on site and defect

— Cure ~95% for low-risk primary BCC

— Stagewise excision with 100% peripheral and deep margin examination by horizontal frozen sections

— Indicated for high-risk BCC: H-zone, recurrent, aggressive histology, ill-defined, large, immunosuppressed, perineural, prior RT site

— Cure rates 97–99% (primary), ~94% (recurrent)—highest of any modality

— Tissue-sparing—critical for eyelid, nasal tip, lip, ear

— Performed under local anesthesia in office setting; same-day reconstruction typical

— Low-risk nodular or superficial BCC on trunk/extremities, not in terminal hair-bearing areas (risk of follicular extension)

— 3 cycles of curettage + electrodessication; heals by second intention with hypopigmented scar

— Cure ~90% in well-selected lesions; operator-dependent

— Reserved for small, superficial, low-risk BCC in patients unable/unwilling to undergo surgery

— Two freeze-thaw cycles; hypopigmentation and scarring common

— Lower cure rates; no histologic margin confirmation

— Continue anticoagulation through Mohs and most excisions

— Prophylactic antibiotics only for high-risk sites (lower extremity, groin, wedge excisions of lip/ear) or endocarditis-risk patients per AHA criteria

— Smoking cessation improves flap/graft survival

Standard surgical excision:

Mohs micrographic surgery (MMS):

Electrodessication and curettage (ED&C):

Cryotherapy (liquid nitrogen):

Photodynamic therapy (PDT) with aminolevulinic acid: alternative for superficial BCC; good cosmesis, multiple sessions

Perioperative pearls:

CCS pearl: Order "Mohs micrographic surgery, dermatology referral" for any biopsy-proven BCC of nose, eyelid, lip, ear, or recurrent lesion; document indication clearly for insurance authorization.

Board pearl: Mohs is cost-effective for high-risk sites because of low recurrence and tissue conservation—Step 3 may test resource utilization framing.

Special Populations — Elderly and Renal/Hepatic Impairment

— BCC is indolent—life expectancy must factor into treatment intensity

— In patients with limited life expectancy (<5–10 years) and small, asymptomatic, low-risk BCC, observation or minimally invasive therapy (topical, ED&C, cryotherapy) is often appropriate

— Avoid extensive reconstructive surgery in patients who cannot tolerate prolonged procedures or anesthesia

— Address goals of care explicitly—cosmesis may matter less than function and avoidance of hospitalization

— Local anesthesia preferred; avoid epinephrine in significant peripheral vascular disease of digits/ears (debated; small risk)

— Screen for anticoagulation, antiplatelets—continue most; manage bleeding with pressure and electrocautery

— Higher risk of wound healing delay—optimize nutrition, glycemic control, smoking cessation

— Falls risk after facial surgery with bulky dressings—consider home health referral

— Topical 5-FU and imiquimod: minimal systemic absorption, generally safe

— Vismodegib and sonidegib: no dose adjustment for mild-moderate renal impairment; limited data in severe CKD/dialysis—use cautiously

— Cemiplimab: no renal dose adjustment; monitor for immune-related nephritis (rising creatinine)

— Vismodegib: avoid in severe hepatic impairment; monitor LFTs at baseline and during therapy

— Sonidegib: similar caution; CK elevation can occur and is concerning in patients with hepatic dysfunction

— Hedgehog inhibitors are CYP3A4 substrates—avoid strong inducers/inhibitors (rifampin, ketoconazole, ritonavir)

— Markedly elevated BCC and SCC risk; consider switching to mTOR inhibitor (sirolimus) in collaboration with transplant team for those with multiple skin cancers

Elderly patients (>75 yo, frail):

Surgical considerations in elderly:

Renal impairment:

Hepatic impairment:

Transplant recipients on calcineurin inhibitors:

Board pearl: In a frail nonagenarian with a 5 mm nodular BCC on the back, active surveillance with photographs is a defensible plan—aggressive surgery is not always patient-centered.

Step 3 management: Explicitly document the shared decision and life-expectancy reasoning in the chart for any "watchful waiting" plan in BCC.

Special Populations — Pregnancy, Pediatrics, and Skin of Color

— BCC is rare in pregnancy; growth is usually slow—defer elective treatment until postpartum when possible

— If treatment needed: surgical excision under local anesthesia (lidocaine ± epinephrine, both pregnancy-compatible) is preferred

— Avoid topical 5-FU (category X), imiquimod (category C—limited data), and hedgehog inhibitors (absolutely contraindicated, teratogenic)

— Radiation therapy avoided

— Counsel against tanning bed use and emphasize sun protection

— BCC in children is rare and should raise concern for an underlying syndrome:

— Gorlin (nevoid BCC) syndrome: AD, PTCH1 mutation; multiple BCCs at young age, odontogenic keratocysts, palmar/plantar pits, calcified falx cerebri, macrocephaly, rib anomalies, medulloblastoma risk

— Xeroderma pigmentosum: AR, defective nucleotide excision repair; severe photosensitivity, early multiple skin cancers (BCC, SCC, melanoma)

— Bazex-Dupré-Christol, Rombo syndromes: rare AD disorders with follicular atrophoderma and multiple BCCs

— Workup for syndromic suspicion: genetic testing, MRI brain (medulloblastoma in Gorlin), panoramic dental imaging

— Management: aggressive sun protection from infancy, avoid radiation therapy in Gorlin, dermatology surveillance every 6 months

— BCC less common but often pigmented and underdiagnosed; delayed presentation worsens outcomes

— Differential includes seborrheic keratosis, melanoma, dermatofibroma—dermatoscopy and biopsy essential

— Cosmetic outcomes complicated by post-inflammatory hyperpigmentation and keloid risk—counsel on scar appearance

Pregnancy:

Pediatrics:

Skin of color (Fitzpatrick IV–VI):

Board pearl: A child with multiple BCCs, jaw cysts, and palmar pits is Gorlin syndrome until proven otherwise—order PTCH1 genetic testing and MRI brain, and avoid all radiation.

Step 3 management: Counsel patients of all skin types that darker skin does not preclude skin cancer; recommend sunscreen and annual skin exams in high-risk individuals regardless of phototype.

Complications and Adverse Outcomes

— "Rodent ulcer" can erode cartilage (ear, nasal ala), bone (skull, orbit), and named vessels

— Functional impairment: eyelid distortion (ectropion, lagophthalmos), nasal collapse, oral incompetence

— Cosmetic disfigurement causing psychosocial distress

— Primary BCC after standard excision: ~5% over 5 years

— Recurrent BCC after re-treatment: ~15–20%—Mohs preferred for any recurrence

— Risk factors: incomplete excision, aggressive histology, H-zone location, immunosuppression

— Most often along V2 (infraorbital), V3 (mental), or facial nerve branches

— Presents as numbness, dysesthesia, weakness; may be silent on imaging early

— Associated with deep recurrence and skull-base extension; requires MRI and often adjuvant radiation

— More likely in basosquamous, large neglected lesions, immunosuppressed hosts

— Spread to regional lymph nodes, lungs, bone; median survival once metastatic historically <1 year (improved with hedgehog inhibitors and cemiplimab)

— Patients with one BCC: ~40–50% develop another within 5 years

— Increased risk of SCC, melanoma, and lip/oral cancers

— Some data suggest modestly elevated risk of non-cutaneous malignancies (controversial)

— Surgical: bleeding, infection, scarring, nerve injury (facial nerve, marginal mandibular), ectropion, alar retraction

— Topical: severe inflammation, secondary infection, pigmentary change

— Hedgehog inhibitors: muscle cramps (treat with calcium, magnesium, hydration; consider amlodipine), alopecia, dysgeusia, weight loss

— Radiation: radiation dermatitis, secondary malignancy, radionecrosis, chronic ulceration

Local destruction—the dominant morbidity of BCC:

Recurrence:

Perineural invasion (PNI):

Metastasis (rare, 0.0028–0.55%):

Multiple primary cancers:

Treatment-related complications:

Board pearl: Persistent numbness or paresthesia in the distribution of a trigeminal branch after BCC treatment is perineural recurrence until proven otherwise—order MRI with contrast and refer urgently.

Step 3 management: Schedule a wound check at 1 week post-op and a clinical recurrence check at 3–6 months for high-risk BCCs.

When to Escalate Care — Consults and Multidisciplinary Triage

— Any suspected BCC requiring biopsy beyond comfort

— Multiple synchronous lesions, atypical presentations, suspected syndromic BCC

— Topical therapy candidates requiring close monitoring

— H-zone lesions, lesions >10 mm on cheek/forehead/scalp/neck or >20 mm on trunk/extremities

— Recurrent BCC, ill-defined borders, aggressive histology, perineural invasion

— Lesions in cosmetically/functionally critical sites (eyelid, lip, nasal ala, ear)

— Immunosuppressed patients with high-risk lesions

— Patients who decline or cannot tolerate surgery

— Adjuvant therapy for PNI, positive margins, large tumors after surgical bed evaluation

— Locally advanced disease in combination with systemic therapy

— Locally advanced BCC not amenable to surgery or radiation

— Metastatic BCC—initiate hedgehog inhibitor; second-line cemiplimab

— Manage immune-related adverse events on PD-1 inhibitors

— Large defects requiring flap or graft reconstruction

— Orbital, nasal, or auricular involvement

— Suspected Gorlin syndrome, xeroderma pigmentosum, or other inherited syndromes

— Family history of multiple BCCs at young age, medulloblastoma, or jaw cysts

— Massive bleeding from eroded lesion (rare)

— Extensive reconstructive surgery requiring general anesthesia and inpatient recovery

— Severe immune-related adverse events on cemiplimab (colitis, pneumonitis, adrenal crisis)

Dermatology referral (the workhorse referral in BCC):

Mohs surgeon referral:

Radiation oncology:

Medical oncology:

Plastic/reconstructive surgery, oculoplastics, ENT:

Genetics:

Hospital admission is rarely needed for BCC itself; consider for:

CCS pearl: For locally advanced disease, the appropriate orders are "dermatology consult, radiation oncology consult, medical oncology consult, multidisciplinary tumor board"—advance the clock and coordinate before initiating therapy.

Board pearl: Don't refer every small BCC to Mohs—a 6 mm nodular BCC on the back is appropriately managed by standard excision in a family medicine or general surgery setting. Match modality to risk to be exam- and value-correct.

Key Differentials — Other Skin Cancers and Premalignant Lesions

— Hyperkeratotic, scaly, sometimes ulcerated papule/plaque on sun-exposed skin

— More likely than BCC to be tender, rapidly growing, and to metastasize (~3–5%)

— Often arises in actinic keratoses; higher risk in transplant recipients (SCC > BCC in SOT)

— Treatment: excision, Mohs for high-risk; cemiplimab for advanced disease

— Rough, scaly, pink/erythematous "sandpaper" papules on sun-damaged skin

— Premalignant—small percent progress to SCC

— Treatment: cryotherapy, topical 5-FU, imiquimod, PDT, tirbanibulin

— Rapidly growing crateriform nodule with central keratin plug; may regress spontaneously

— Considered well-differentiated SCC variant—treat with excision

— Asymmetric, irregular borders, color variation, diameter >6 mm, evolving (ABCDE)

— Pigmented BCC can mimic melanoma—dermoscopy and biopsy distinguish

— Critical to differentiate: melanoma metastasizes early; full-thickness biopsy required

— Rapidly growing, firm, red-purple nodule on sun-exposed skin in elderly/immunosuppressed

— Aggressive; high metastatic rate; AEIOU mnemonic (asymptomatic, expanding rapidly, immunosuppression, older than 50, UV-exposed)

— Well-demarcated, erythematous, scaly plaque; mimics superficial BCC

— Biopsy distinguishes; treat with topical 5-FU, imiquimod, ED&C, or excision

Squamous cell carcinoma (SCC):

Actinic keratosis (AK):

Keratoacanthoma:

Melanoma:

Merkel cell carcinoma:

Bowen disease (SCC in situ):

Key distinction: Pearly translucency with arborizing telangiectasias = BCC; hyperkeratotic, scaly, tender = SCC/AK; pigment heterogeneity with atypical network = melanoma. Dermatoscopy resolves most.

Board pearl: Solid organ transplant recipients flip the BCC:SCC ratio—they get more SCC than BCC, and their SCCs behave more aggressively with higher metastatic potential. Surveillance and education are critical.

Step 3 management: Any pigmented lesion with asymmetry or color variation gets a full-thickness biopsy (punch or excisional)—never shave a possible melanoma, as it precludes accurate Breslow depth measurement.

Key Differentials — Benign Mimickers

— Yellowish, soft, umbilicated papules on forehead/cheeks in middle-aged/older adults

— Crown of vessels around a central yellow lobule on dermatoscopy (vs arborizing for BCC)

— Benign; no treatment needed; can be removed cosmetically with cautery

— Soft, flesh-colored, dome-shaped papule; stable over time

— Lacks pearly translucency and telangiectasias; dermoscopy shows comma vessels

— Reassurance; biopsy if changing

— Firm, dome-shaped, skin-colored papule on the nose; stable, benign

— Histologically angiofibroma; may biopsy to confirm if uncertain

— Pearly, dome-shaped papules with central umbilication; usually in children or immunosuppressed

— Multiple lesions; viral etiology (poxvirus); self-limited

— "Stuck-on" waxy, warty, brown/black plaques; horn pseudocysts on dermoscopy

— Benign; leser-Trélat sign (sudden eruption) raises concern for internal malignancy

— Friable, bleeding red papule, often post-trauma or in pregnancy

— Rapidly grows; treat with excision or curettage

— Firm, pigmented papule on extremities with dimple sign on lateral compression

— Benign; biopsy if atypical

— Nummular eczema, psoriasis, tinea corporis—respond to appropriate topical therapy; persistence despite treatment warrants biopsy

— Bowen disease and superficial BCC look similar—biopsy any "eczema patch" not resolving after 4–6 weeks of topical steroids

Sebaceous hyperplasia:

Intradermal melanocytic nevus:

Fibrous papule of the nose:

Molluscum contagiosum:

Seborrheic keratosis:

Pyogenic granuloma:

Dermatofibroma:

Inflammatory mimickers (for superficial BCC):

Key distinction: A lesion that fails to resolve with topical steroids is not eczema—biopsy is the next step. This is a classic Step 3 stem where the wrong answer is "try another topical."

Board pearl: Stretch the skin under bright light or use dermoscopy on any suspicious facial papule—pearly translucency and arborizing vessels unmask BCC hiding among benign mimics.

Secondary Prevention and Long-Term Plan

— Broad-spectrum SPF 30+ sunscreen daily to sun-exposed areas; reapply every 2 hours when outdoors

— Avoid sun 10 AM–4 PM; seek shade; wear wide-brim hats, UPF clothing, sunglasses

— No tanning beds—WHO Group 1 carcinogen; risk especially high in <35 yo users

— Counsel on vitamin D supplementation if sun avoidance creates deficiency risk

— Monthly self-checks using a full-length mirror and handheld mirror for posterior areas

— Look for new, changing, non-healing lesions; involve partner for hard-to-see areas

— Nicotinamide (vitamin B3) 500 mg PO BID: reduces NMSC incidence ~23% in patients with prior NMSC (ONTRAC trial); inexpensive, well-tolerated

— Topical 5-FU field therapy or imiquimod for diffuse actinic damage

— Acitretin (oral retinoid) for transplant recipients with multiple SCCs/BCCs—dermatology-directed

— In transplant patients, consider switching to mTOR inhibitor (sirolimus) with transplant team

— Smoking cessation (worse wound healing, possible SCC risk)

— Address arsenic exposure (well water testing)

— Optimize immunosuppression minimization in transplant patients

— Annual full-body skin exam for patients with one prior BCC

— Every 6 months for high-risk patients (multiple prior NMSC, transplant, Gorlin, XP)

— Every 3–4 months in first year after a high-risk BCC, then space out

Sun protection counseling—core to every visit:

Self-skin examination:

Chemoprevention for high-risk patients:

Modifiable risk factor management:

Long-term surveillance schedule:

Board pearl: Nicotinamide (not niacin) is the chemoprevention agent—niacin causes flushing and is a different vitamer; nicotinamide does not.

Step 3 management: At every BCC follow-up, document sun protection counseling, self-skin exam education, and chemoprevention discussion if appropriate—these are quality measures and exam-favored answers.

Follow-Up, Monitoring, and Patient Counseling

— Low-risk BCC: skin exam every 6–12 months for 5 years, then annually for life

— High-risk BCC: every 3–6 months for 1–2 years, every 6–12 months for years 3–5, then annually

— Earlier visit at 1–2 weeks for wound check and suture removal if applicable

— Inspect prior surgical scar for recurrence (new papule, induration, telangiectasia, ulceration)

— Palpate regional lymph nodes

— Examine entire skin surface for new primary lesions

— Dermatoscopy of suspicious areas; consider total-body photography in high-risk patients

— Petrolatum (not antibiotic ointment) on healing wounds—reduces contact dermatitis from neomycin/bacitracin

— Sun protection of scar for 6–12 months to prevent post-inflammatory hyperpigmentation

— Silicone gel sheets or massage for hypertrophic scars

— Realistic expectation setting for facial scars

— Vismodegib/sonidegib: baseline and periodic LFTs, CK; pregnancy testing monthly during and for 24 months after (vismodegib); manage muscle cramps with hydration, electrolytes, amlodipine

— Cemiplimab: monitor for immune-related AEs—TSH, cortisol, glucose, LFTs, creatinine, pulmonary symptoms every cycle

— Address anxiety about disfigurement, recurrence, and additional cancers

— Refer to skin cancer support groups when appropriate

— Address body image and depression especially after facial reconstruction

— Provide written instructions on warning signs of recurrence

— Demonstrate self-skin exam technique with handouts/photos

— Use EHR patient portal for photo submissions of new concerns between visits (telederm where available)

Post-treatment follow-up cadence (NCCN-aligned):

Monitoring parameters:

Wound and scar care counseling:

Monitoring on systemic therapy:

Psychosocial counseling:

Patient education materials:

Board pearl: Use petrolatum, not topical antibiotics, on clean surgical wounds—routine antibiotic ointment increases contact dermatitis without reducing infection in clean cases.

Step 3 management: Build a surveillance calendar in the EHR at the time of BCC diagnosis—lapses in follow-up are the most common preventable contributor to recurrence and new primary cancers.

Ethical, Legal, and Patient Safety Considerations

— Discuss diagnosis (or working differential), procedure, alternatives, risks (bleeding, infection, scar, nerve injury), benefits, and option to decline

— For Mohs: explain stagewise nature, possibility of multiple stages, reconstructive planning, scar expectations

— Document in chart; use teach-back to confirm understanding

— Special case: in patients with cognitive impairment, identify and document the healthcare proxy/surrogate; do not proceed with non-emergent surgery without proper consent

— Discuss life expectancy and goals of care openly; "watchful waiting" is ethically valid for low-risk lesions in patients with limited life expectancy

— Avoid over-treatment driven by reflex rather than patient preference

— Vismodegib/sonidegib are REMS drugs—mandatory pregnancy testing, contraception counseling, and acknowledgment forms

— Counsel both male and female patients; semen carries drug, condoms required

— No blood/sperm donation during and for months after therapy

— When referring to Mohs or specialist, send biopsy report, photographs, medication list, anticoagulation status in a structured handoff

— Confirm appointment scheduling before leaving the visit; close the loop on "no-shows" to high-risk consults

— Failure to follow up on a positive biopsy is a common malpractice claim—use EHR result-tracking tools

— Mohs and dermatology access is uneven; for rural/underserved patients, consider telederm triage and prioritize high-risk lesions

— Discuss cost: Mohs is more expensive than standard excision but more cost-effective for appropriate indications

— Many states prohibit minors from using tanning beds—reinforce this counseling and report violations where applicable

— Document all sun-protection counseling; some quality measures track this

Informed consent for biopsy and surgery:

Shared decision-making in elderly/frail patients:

Teratogenicity and contraception (hedgehog inhibitors):

Transitions of care:

Health systems and access:

Tanning bed legislation:

Mandatory disclosure:

Board pearl: A patient with a positive BCC biopsy who never returns for treatment requires documented outreach attempts (calls, letters, certified mail for high-risk lesions)—this is the standard of care and protects against liability while supporting the patient.

High-Yield Associations and Rapid-Fire Facts

Most common cancer in humans—BCC; ~80% of nonmelanoma skin cancers.

Pearly papule + arborizing telangiectasias + central ulcer on the face = BCC.

Hedgehog pathway: BCC pathogenesis driven by PTCH1 loss or SMO activation; targeted by vismodegib/sonidegib.

Gorlin syndrome: PTCH1, AD, multiple BCCs, odontogenic keratocysts, palmar/plantar pits, calcified falx cerebri, macrocephaly, medulloblastoma. No radiation therapy.

Xeroderma pigmentosum: AR, nucleotide excision repair defect, severe photosensitivity, early skin cancers.

H-zone of the face: high-risk anatomic sites mandating Mohs.

Mohs cure rates: 97–99% primary, ~94% recurrent.

Standard excision margins for low-risk BCC: 4 mm.

Topical 5-FU and imiquimod: superficial BCC on trunk/extremities only; not facial nodular lesions.

Vismodegib triad: muscle spasms, alopecia, dysgeusia.

Cemiplimab: anti-PD-1 for advanced BCC after hedgehog inhibitor failure.

Nicotinamide 500 mg BID: reduces NMSC incidence in high-risk patients (ONTRAC).

Transplant recipients: SCC > BCC; 5–10× elevated risk; switch to mTOR inhibitor (sirolimus) if multiple cancers.

Perineural invasion: order MRI; consider adjuvant radiation; trigeminal branches most common.

Pigmented BCC: mimics melanoma; common in skin of color; dermoscopy shows blue-gray ovoid nests, leaf-like areas.

Basosquamous carcinoma: hybrid; higher metastatic risk; treat aggressively.

Metastasis rate: <0.1%—BCC almost never metastasizes.

Continue anticoagulation through skin biopsy and Mohs.

Petrolatum, not antibiotic ointment, on clean surgical wounds.

Tanning beds: WHO Group 1 carcinogen.

40–50%: 5-year risk of a second NMSC after the first.

ED&C: avoid in terminal hair-bearing areas (follicular extension).

Recurrence at scar: telangiectasia, induration, ulceration—biopsy.

Board pearl: When a question gives you "pearly papule on the nose of a 65-year-old farmer," the answer to "next step" is biopsy, and to "best definitive treatment" is Mohs surgery—two distinct, sequential answers that examinees often conflate.

Board Question Stem Patterns

— "A 72-year-old fair-skinned man with a history of outdoor work presents with a slowly enlarging, pearly papule on the right nasal ala that occasionally bleeds. There is a central ulcer with rolled, telangiectatic borders." → Answer: Shave biopsy, then Mohs surgery for definitive treatment.

— "A 60-year-old has a 4 cm well-demarcated, scaly, erythematous patch on her back for 8 months, unresponsive to topical hydrocortisone." → Punch biopsy; likely superficial BCC (or Bowen disease).

— "A 14-year-old presents with two new pearly papules on the face. He has macrocephaly, palmar pits, and a jaw cyst was removed at age 12." → Gorlin syndrome (PTCH1); order MRI brain (medulloblastoma), avoid radiation therapy.

— "A 58-year-old kidney transplant recipient on tacrolimus has multiple new skin lesions over 2 years." → Risk of SCC > BCC; consider switch to sirolimus, intensify surveillance, sun protection.

— "Six months after excision of a forehead BCC, the patient develops numbness over the forehead and ipsilateral diplopia." → MRI with contrast of the face/skull base for perineural recurrence along V1.

— "A 78-year-old on warfarin (INR 2.3) for atrial fibrillation needs Mohs surgery for a nasal BCC." → Continue warfarin; do not stop.

— "A patient with locally advanced inoperable BCC starts vismodegib and develops severe muscle cramps and hair loss." → Known adverse effects; supportive care (hydration, electrolytes, amlodipine); continue if tolerated; counsel on strict contraception and no blood donation.

— "A 70-year-old with three prior BCCs asks how to reduce future risk." → Nicotinamide 500 mg BID, sun protection, annual skin exams.

— Small superficial BCC on the back: topical 5-FU or excision.

— Nodular BCC on the cheek <1 cm: standard excision with 4 mm margins.

— Recurrent BCC on the nasal tip: Mohs.

The classic recognition stem:

The eczema-that-isn't stem:

The Gorlin syndrome stem:

The transplant patient stem:

The perineural invasion stem:

The anticoagulation stem:

The hedgehog inhibitor stem:

The chemoprevention stem:

The modality-selection stem:

Board pearl: Step 3 stems frequently test the sequence: recognize → biopsy → risk stratify → choose modality → arrange follow-up and chemoprevention. Identify which step the question is testing before picking an answer.

One-Line Recap

Basal cell carcinoma is a slow-growing, locally destructive but rarely metastatic skin cancer of UV-exposed sites that is recognized clinically as a pearly papule with arborizing telangiectasias, confirmed by skin biopsy, risk-stratified by site/size/histology/host, and treated with surgery (Mohs for high-risk and cosmetically critical areas, standard excision with 4 mm margins for low-risk), topical therapy for select superficial trunk/extremity lesions, or hedgehog inhibitors and cemiplimab for advanced disease, with lifelong sun protection, self-exams, and surveillance.

Recognize: pearly papule + arborizing telangiectasias + non-healing ulcer on sun-exposed skin → biopsy; superficial BCC mimics treatment-resistant eczema on the trunk.

Stratify and treat: low-risk → excision with 4 mm margins or topical/ED&C; high-risk (H-zone, large, recurrent, aggressive histology, immunosuppressed, PNI) → Mohs surgery; locally advanced/metastatic → vismodegib/sonidegib, then cemiplimab.

Don't miss: Gorlin syndrome in young patients with multiple BCCs (no radiation), perineural invasion presenting as facial numbness (MRI), transplant recipients (SCC > BCC, consider sirolimus), continue anticoagulation through biopsy and Mohs.

Prevent and follow: sun protection, no tanning beds, nicotinamide 500 mg BID for high-risk patients, annual full-body skin exam (every 3–6 months if high-risk), self-exams monthly, and a documented surveillance schedule because 40–50% of patients develop a second NMSC within 5 years.

Step 3 management: Always pair the definitive treatment answer with a follow-up cadence, chemoprevention discussion, and sun-protection counseling—Step 3 rewards longitudinal, ambulatory thinking over single-encounter decisions.