# Melanoma Staging and Breslow Thickness

> Melanoma staging for NEET-PG Dermatology covering Breslow thickness, Clark level, ulceration, sentinel node biopsy criteria and the excision margin for each T category.

- Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/melanoma-staging-and-breslow-thickness
- Exam / course: NEET-PG · Subject: Dermatology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Rook's Textbook of Dermatology; AJCC Cancer Staging Manual; NCCN Guidelines for Melanoma
- How to cite: "Melanoma Staging and Breslow Thickness", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/melanoma-staging-and-breslow-thickness

## Direct answer

Melanoma staging depends mainly on Breslow thickness, the vertical distance from the granular layer of the epidermis to the deepest invasive melanoma cell. Thicker and ulcerated lesions have a worse prognosis and need wider excision, and sentinel node biopsy is offered for lesions thicker than 1 mm and discussed for T1b lesions (0.8 mm or more, or any ulcerated T1). Clark level is now a secondary descriptor.

## What you must remember

- **Breslow thickness:** measured with an ocular micrometer from the granular layer, or from the ulcer base if ulcerated, to the deepest tumour cell; it is the single most important prognostic factor in localised melanoma.
- **Clark level:** anatomical levels I (in situ) to V (subcutaneous fat); levels IV and V are high risk, but thickness is preferred for staging.
- **Ulceration:** breach of the epidermis over the tumour; it changes the T category to the b subclass and worsens survival at any thickness.
- **Mitotic rate:** mitoses per mm² in the dermis; it adds prognostic information for thin lesions even though it does not define the T category.
- **T category cut-offs:** T1 up to 1 mm, T2 1.01 to 2 mm, T3 2.01 to 4 mm and T4 above 4 mm, per the AJCC system.
- **Excision margins:** in situ melanoma 5 mm to 1 cm; up to 1 mm thick 1 cm; 1.01 to 2 mm 1 to 2 cm; over 2 mm 2 cm.
- **Sentinel node biopsy:** a staging procedure using radiocolloid and blue dye for T2 and higher lesions and discussed for T1b; it stages the nodes and does not treat disease.

## Staging by thickness and ulceration

Use the T category to decide how wide to excise and whether to stage the regional nodes. The table links thickness, ulceration and the usual sentinel node decision.

| T category | Breslow thickness | Ulceration | Sentinel node biopsy |
|---|---|---|---|
| T1a | Below 0.8 mm | Absent | Not routinely offered |
| T1b | 0.8 to 1.0 mm, or below 0.8 mm with ulceration | Present or absent | Discussed and considered |
| T2 | 1.01 to 2.0 mm | Absent (a) or present (b) | Offered |
| T3 | 2.01 to 4.0 mm | Absent (a) or present (b) | Offered |
| T4 | Above 4.0 mm | Absent (a) or present (b) | Offered |

The a and b suffix marks absent or present ulceration, so T2b behaves worse than T2a. Node status found on sentinel biopsy then fixes the N category and guides adjuvant decisions. Shave biopsies can underestimate thickness, so a re-excision with the planned margin is usually undertaken.

## Where thickness-based staging goes wrong in exams

Vignettes often hinge on one measurement, so a wrong number leads to a wrong margin.

- **Trap:** choosing a 1 cm margin for a 1.5 mm lesion because it looks small. **Correct:** a thickness of 1.01 to 2 mm calls for a 1 to 2 cm margin, so check the reported Breslow value first.
- **Trap:** measuring thickness from the surface of a crusted lesion. **Correct:** measure from the granular layer, or from the ulcer base if ulcerated, as the histology report defines.
- **Trap:** offering sentinel node biopsy to every melanoma regardless of depth. **Correct:** thin T1a lesions usually skip it, while T2 and higher lesions are the usual candidates and T1b is a discussion.
- **Trap:** calling Clark level the main prognostic factor. **Correct:** Breslow thickness is the preferred measure, and Clark level adds less prognostic value.

## Frequently asked questions

### Which measurement is the most important prognostic factor in localised cutaneous melanoma?

Breslow thickness is the most important prognostic factor in localised cutaneous melanoma, followed by ulceration and nodal status. It is measured in millimetres on histopathology and decides the T category, the excision margin and the need for sentinel node biopsy.

### What excision margin is used for a melanoma of 1.5 mm Breslow thickness?

A 1.5 mm melanoma falls in the T2 range, for which a surgical margin of 1 to 2 cm is standard. Margins are measured from the edge of the lesion or the biopsy scar, and the final width depends on the histological Breslow thickness.

### Does ulceration change melanoma staging?

Ulceration changes melanoma staging by adding the b suffix to the T category and worsening prognosis at any given thickness. A thin ulcerated melanoma below 0.8 mm is classed as T1b rather than T1a.

### When is sentinel lymph node biopsy indicated in melanoma?

Sentinel node biopsy is offered for melanomas of T2 and higher and discussed for T1b, that is lesions 0.8 to 1.0 mm or thin ulcerated lesions. It stages the regional nodes using radiocolloid and blue dye, and it does not itself treat the primary tumour.

### Why is a shave biopsy avoided for suspected melanoma?

A shave biopsy can leave part of the tumour behind and underestimate Breslow thickness, which distorts both the T category and the excision margin. An excisional or narrow incisional biopsy gives a reliable depth measurement for melanoma.