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Skin cancer — melanoma, BCC and SCC
In melanoma the Breslow thickness sets the excision margins and the need for sentinel node biopsy; BCC is common and local and is treated by excision (or Mohs on the face), and SCC is linked to sun exposure, immunosuppression and chronic scars and can metastasise.
Why it matters in the exam
The exam usually presents a suspicious mole, and the first question is how to biopsy it: a full-thickness excision of the whole lesion with a narrow margin of 1–3 mm, so the pathologist can measure the Breslow thickness, the most important prognostic factor. Then the final excision margins by thickness are asked, and sentinel node biopsy, which is considered from 0.8 mm or with ulceration. Early detection rests on the ABCDE signs: asymmetry, irregular border, uneven colour, diameter above 6 mm and evolution over time.
Candidates are also asked about a positive sentinel node — now managed by ultrasound surveillance instead of routine dissection — and about adjuvant immunotherapy in advanced stages. BCC is the most common skin cancer: a "pearly" nodule with rolled edges and vessels, which almost never metastasises and is treated by excision with margins of about 4 mm or by Mohs surgery on the face. SCC is linked to actinic keratosis, organ-transplant recipients and old burn scars (Marjolin's ulcer), and is excised with wider margins; sentinel node biopsy is not routine.
Key points
- Full-thickness excisional biopsy with 1–3 mm margins.
- Breslow sets the margin: 0.5–1 cm for in situ; 1 cm when thickness is up to 1 mm; 1–2 cm at 1–2 mm; 2 cm beyond 2 mm.
- Sentinel node biopsy from 0.8 mm or with ulceration; positive node — usually surveillance, not dissection.
- BCC — local, excision or Mohs.
- SCC — actinic keratosis, immunosuppression, Marjolin; wider margins.
Summary table
| Situation | Finding | Treatment |
|---|---|---|
| Melanoma in situ | No dermal invasion | Excision with 0.5–1 cm margins |
| Melanoma up to 1 mm | Breslow up to 1 mm | 1 cm margins; sentinel node biopsy considered from 0.8 mm or with ulceration |
| Melanoma 1–2 mm | Breslow 1–2 mm | 1–2 cm margins and sentinel node biopsy |
| Melanoma over 2 mm | Breslow over 2 mm | 2 cm margins, sentinel node biopsy; adjuvant immunotherapy in advanced stages |
| BCC | "Pearly" nodule, rolled edges, vessels; almost no metastases | Excision with about 4 mm margins or Mohs on the face |
| SCC | Actinic keratosis, immunosuppression, chronic scar (Marjolin) | Excision with margins of 4–6 mm or more; Mohs in sensitive areas |
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Sources
- NCCN Clinical Practice Guidelines in Oncology: Melanoma: Cutaneous, 2025 — Biopsy, excision margins, sentinel node biopsy and adjuvant therapy
- NCCN Clinical Practice Guidelines in Oncology: Basal Cell and Squamous Cell Skin Cancers, 2025 — Excision margins and Mohs surgery
- Sabiston Textbook of Surgery, 21st edition (2022) — Melanoma and Cutaneous Malignancies
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.