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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- BCC is the most common human malignancy and is strongly linked to cumulative and intermittent UV exposure
- Classic lesion: pearly or translucent papule with rolled border, arborizing telangiectasias, and possible central ulceration
- It grows slowly, invades locally, and very rarely metastasizes
- Diagnosis is by shave, punch, or excisional biopsy; treatment is usually surgical excision or Mohs for high-risk sites
- High-risk facial H-zone lesions, recurrent tumors, aggressive histology, and immunosuppression warrant dermatology/Mohs referral
Overview
Basal cell carcinoma is a keratinocyte carcinoma derived from basal epidermal cells or follicular structures. It is the most common skin cancer in the United States. BCC is clinically important because it is common, frequently occurs on cosmetically sensitive sun-exposed areas, and can cause extensive local tissue destruction if neglected. Histologic subtypes include nodular, superficial, morpheaform/sclerosing, infiltrative, micronodular, and pigmented BCC. Step 2 CK classically contrasts BCC with squamous cell carcinoma and melanoma: BCC is pearly and telangiectatic, SCC is scaly/hyperkeratotic and more metastatic, melanoma is pigmented and depth-driven.
Epidemiology
BCC is most common in older, fair-skinned adults and occurs most often on the head and neck. Risk factors include UV exposure, indoor tanning, fair skin, prior radiation, arsenic exposure, immunosuppression, and genetic syndromes such as basal cell nevus syndrome (Gorlin syndrome). The incidence rises with age but BCC can occur in younger adults with heavy UV exposure. Metastatic BCC is extremely rare, but neglected lesions can erode cartilage, bone, eyelids, nose, and perineural structures.
Clinical Features
Symptoms
Slowly enlarging papule, nodule, or plaque on sun-exposed skin
Lesion that bleeds, crusts, heals, then bleeds again
Nonhealing sore on the nose, eyelid, ear, scalp, or face
Usually painless and asymptomatic; may itch or feel tender if ulcerated
Signs
Pearly translucent papule with rolled border and arborizing telangiectasias
Central ulceration with raised rolled edge (rodent ulcer)
Superficial BCC: thin erythematous scaly patch on trunk, often mistaken for eczema or psoriasis
Morpheaform BCC: scar-like indurated plaque with ill-defined borders and higher recurrence risk
Periocular, nasal, ear, lip, or H-zone facial location is high risk
Investigations
First-line
Skin examinationAssess lesion morphology, size, borders, anatomic risk site, and signs of perineural involvement; examine for additional keratinocyte cancers
BiopsyShave biopsy is common for raised lesions; punch biopsy may be used for infiltrative plaques; excisional biopsy for small lesions where complete removal is practical
HistologyBasaloid tumor nests with peripheral palisading and retraction artifact; subtype influences risk and treatment choice
Second-line
DermoscopyMay show arborizing vessels, blue-gray ovoid nests, ulceration, maple-leaf-like areas; useful adjunct but histology confirms diagnosis
Risk stratificationHigh-risk features include facial H-zone, size, recurrent tumor, immunosuppression, poorly defined borders, aggressive histology, or perineural symptoms
Specialist
ImagingRarely needed; consider MRI/CT if deep invasion, perineural spread, orbital involvement, or bone invasion is suspected
Management
AAD Basal Cell Carcinoma Guideline1
Low-risk BCC
- Standard surgical excision with histologic margin assessment is first-line for most low-risk tumors
- Electrodesiccation and curettage may be used for selected low-risk non-hair-bearing sites
- Topical imiquimod or 5-fluorouracil may be considered for selected superficial BCC when surgery is not preferred, but recurrence risk is higher than surgery
- Cryosurgery may be considered only for selected low-risk lesions when biopsy has established diagnosis and surgery is unsuitable
2
High-risk BCC
- Mohs micrographic surgery is preferred for high-risk facial sites, recurrent tumors, aggressive histology, and tissue-sparing areas
- Refer urgently for periocular, nasal, lip, ear, genital, recurrent, morpheaform, or poorly defined lesions
- Radiation therapy can be used when surgery is contraindicated or declined, particularly in older patients
3
Advanced disease
- Locally advanced or metastatic BCC: hedgehog pathway inhibitors such as vismodegib or sonidegib may be used by oncology/dermatology
- PD-1 inhibitor cemiplimab may be considered after hedgehog inhibitor failure or intolerance
4
Prevention and surveillance
- Sun protection, avoidance of indoor tanning, and self-skin examination
- Regular dermatologic follow-up because one keratinocyte carcinoma predicts future BCC/SCC
- Counsel high-risk patients, especially immunosuppressed patients, on early evaluation of nonhealing lesions
Complications
- Local tissue destruction: Neglected BCC can invade cartilage, bone, orbit, and perineural planes
- Recurrence: Higher with aggressive histology, incompletely excised lesions, and high-risk facial sites
- Multiple future skin cancers: Prior BCC substantially increases risk of additional keratinocyte carcinomas
- Cosmetic and functional morbidity: Especially on nose, eyelids, lips, and ears
- Metastasis: Extremely rare but possible in very advanced or neglected disease
USMLE Step 2 CK Exam Tips
- 1Pearly papule + telangiectasias + rolled border = basal cell carcinoma
- 2BCC is the most common human cancer and rarely metastasizes; it is locally destructive
- 3Rodent ulcer on sun-exposed face is classic BCC
- 4Superficial BCC can mimic eczema on the trunk; persistent scaly plaque needs biopsy
- 5High-risk facial H-zone lesion = Mohs surgery, not routine destructive treatment
- 6Gorlin syndrome = multiple BCCs, odontogenic jaw cysts, palmar pits, calcified falx cerebri
- 7Biopsy first; do not treat a suspected skin cancer blindly with topical steroid
practicetest your knowledge on basal cell carcinomaApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — dermatology and beyond.
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