Skin cancer is the most common cancer in the United States. The clinical skill is not memorizing every lesion type — it is recognizing the features that demand biopsy rather than watchful waiting, and knowing which biopsy technique preserves staging accuracy. When in doubt, biopsy.
CLINICAL PRINTABLE
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A one-page Skin Cancer Warning Signs clinical reference is on the way.
1 · Recognition / Warning Signs
- ABCDE criteria for melanoma: Asymmetry, Border irregularity, Color variation (multiple shades of brown, black, red, white, blue), Diameter >6 mm, Evolution (any change in size, shape, color, or new symptom). Any single criterion warrants evaluation.
- Basal cell carcinoma (BCC): most common skin cancer. Pearly or translucent papule with rolled borders and telangiectasias. May ulcerate centrally ('rodent ulcer'). Sun-exposed areas. Rarely metastasizes but causes significant local destruction.
- Squamous cell carcinoma (SCC): scaly, erythematous plaque or nodule that may ulcerate. Arises from actinic keratoses (premalignant) or de novo. Higher metastatic potential than BCC, especially on the lip, ear, and in immunocompromised patients.
- Melanoma: asymmetric pigmented lesion with irregular borders and color variation. Subtypes: superficial spreading (most common), nodular (rapidly growing, often amelanotic), lentigo maligna (slow-growing, sun-damaged skin in elderly), acral lentiginous (palms, soles, subungual — occurs in all skin types).
- Actinic keratosis (AK): rough, scaly patch on sun-damaged skin. Premalignant — risk of progression to SCC. Treat to prevent malignant transformation. Multiple AKs indicate field cancerization.
- Ugly duckling sign: a lesion that looks different from the patient's other nevi ('the odd one out'). This is a practical clinical tool — a lesion that stands out from the patient's baseline pattern warrants evaluation regardless of ABCDE criteria.
2 · Differential / Benign Mimics
Seborrheic keratosis
Benign, 'stuck-on' waxy papule or plaque. Brown to black. Common in older adults. Horn cysts visible on dermoscopy. No malignant potential — but can mimic melanoma clinically.
Dermatofibroma
Firm, hyperpigmented papule on the lower extremity. Dimple sign: pinching the lesion causes central dimpling. Benign — no treatment required unless symptomatic.
Pyogenic granuloma
Rapidly growing, friable, vascular papule that bleeds easily. Common after minor trauma. Benign but can mimic amelanotic melanoma — biopsy if uncertain.
Merkel cell carcinoma
Rapidly growing, flesh-colored or violaceous nodule on sun-exposed skin in elderly or immunocompromised patients. Aggressive — high metastatic potential. Biopsy any rapidly growing skin nodule.
3 · Treatment Pathway
Actinic keratosis — treatment
Cryotherapy (liquid nitrogen) for individual lesions. Field therapy for multiple lesions: topical 5-fluorouracil (5-FU), imiquimod, ingenol mebutate, or photodynamic therapy (PDT). Annual skin exam for patients with multiple AKs.
Basal cell carcinoma — treatment
Excision with 4 mm margins for low-risk BCC. Mohs micrographic surgery for high-risk locations (face, ears, nose), large tumors, recurrent BCC, or poorly defined borders. Topical imiquimod or 5-FU for superficial BCC in low-risk locations.
Squamous cell carcinoma — treatment
Excision with 4–6 mm margins for low-risk SCC. Mohs surgery for high-risk locations, large tumors, poorly differentiated histology, or perineural invasion. Sentinel lymph node biopsy for high-risk SCC. Radiation for unresectable disease or adjuvant therapy.
Melanoma — treatment by stage
Wide local excision with margins based on Breslow thickness (1 mm thick: 2 cm margins). Sentinel lymph node biopsy for melanoma >0.8 mm or with ulceration. Stage III–IV: immunotherapy (checkpoint inhibitors: pembrolizumab, nivolumab) or targeted therapy (BRAF/MEK inhibitors for BRAF-mutant melanoma).
Biopsy approach
Excisional biopsy preferred for suspected melanoma — removes the entire lesion for accurate Breslow thickness measurement. A sufficiently deep saucerization may be appropriate when excision is not feasible. Shave biopsy is acceptable for suspected BCC/SCC. Punch biopsy for lesions where excision is impractical. For suspected melanoma, ensure adequate depth for diagnosis and staging.
4 · Expected Response / Surveillance
- AK treatment: cryotherapy clears individual lesions. Field therapy with 5-FU or imiquimod causes significant local reaction (erythema, crusting, erosion) — this is expected and indicates treatment efficacy. Reassess at 4–8 weeks.
- BCC/SCC after excision: recurrence rates are low with adequate margins. Annual skin exam for 5 years. Patients with one BCC/SCC have significantly increased risk of subsequent skin cancers.
- Melanoma surveillance: follow-up frequency based on stage. Stage I–II: every 6–12 months for 5 years, then annually. Stage III–IV: every 3–6 months. Teach patients self-skin examination.
5 · Escalation
- Any suspicious pigmented lesion: dermatology referral for dermoscopy and biopsy. Do not watch a lesion that meets ABCDE criteria or the ugly duckling sign.
- Melanoma confirmed on biopsy: urgent dermatology/oncology referral for staging workup and wide local excision planning. Do not delay.
- High-risk SCC (lip, ear, immunocompromised host, perineural invasion, poorly differentiated): dermatology or surgical oncology referral for Mohs surgery and lymph node evaluation.
- Rapidly growing skin nodule in elderly or immunocompromised patient: biopsy urgently — Merkel cell carcinoma and other aggressive tumors can present this way.
Apply It · Change One Detail
APPLY IT
A 58-year-old man with a history of significant sun exposure presents with a 7 mm pigmented lesion on his back. It has multiple shades of brown and black, irregular borders, and his wife noticed it has changed over the past 3 months. This lesion meets multiple ABCDE criteria and has evolved. It requires excisional biopsy, not watchful waiting. The appropriate response is referral for biopsy, not a 3-month follow-up.
CHANGE ONE DETAIL
Change one detail — the same patient has a 4 mm uniformly tan, symmetric, round lesion with smooth borders that has been present and unchanged for years. This is a stable, benign-appearing nevus. Annual skin exam and patient education about self-monitoring are appropriate. The key word is 'unchanged' — evolution is the most important feature to track.
Bottom Line
When in doubt, biopsy. The cost of a biopsy is far lower than the cost of a missed melanoma. For suspected melanoma, obtain a complete biopsy with adequate depth for diagnosis and Breslow measurement; excisional biopsy is preferred when feasible.
EVIDENCE & REFERENCES
- Swetter SM, et al. Guidelines of care for the management of primary cutaneous melanoma. J Am Acad Dermatol. 2019;80(1):208-250. doi:10.1016/j.jaad.2018.08.055
- Work Group; Invited Reviewers, et al. Guidelines of care for the management of basal cell carcinoma. J Am Acad Dermatol. 2018;78(3):540-559. doi:10.1016/j.jaad.2017.10.006