Recallab › Question bank › Dermatology › #50160
Melanoma prognosis
Which single factor is the most important predictor of prognosis in a primary cutaneous melanoma?
- A. Clark level of invasion
- B. Diameter of the lesion
- C. Degree of colour variation
- correctD. Breslow thickness
Explanation
Key fact
Breslow thickness - depth in millimetres from the granular layer to the deepest tumour cell - is the strongest prognostic factor and drives both staging and excision margins.
Breslow thickness. It is a direct measurement, reproducible between pathologists, and it predicts survival better than anything else.
Why
Melanoma spreads by depth, not by surface area.
Breslow measures depth in millimetres with an ocular micrometer.
Being a continuous measurement, it is far more reproducible than a category.
It determines the T stage and therefore the surgical excision margin.
It also decides whether a sentinel lymph node biopsy is offered.
Breslow thickness and excision margin
| Thickness | Recommended margin |
|---|---|
| In situ | 0.5 to 1 cm |
| Up to 1 mm | 1 cm |
| 1 to 2 mm | 1 to 2 cm |
| Over 2 mm | 2 cm |
Depth in millimetres, not width on the surface
Why not the others
- A. Clark level of invasion — grades depth by anatomical layer - papillary dermis, reticular dermis and so on. It is less reproducible and has been dropped from staging in favour of Breslow.
- B. Diameter of the lesion — is part of the ABCDE screening rule for recognising melanoma, but surface size does not predict outcome.
- C. Degree of colour variation — again helps recognition, not prognosis.
Remember
Depth, not width. A small dark lesion that has grown downwards is far more dangerous than a large flat one.
Go deeper
Ulceration and mitotic rate are the other independent prognostic factors, and ulceration upstages a tumour of any thickness.
Superficial spreading melanoma is the commonest type worldwide, but acral lentiginous melanoma - on palms, soles and under nails - is the commonest in Indian and other darker-skinned populations and is often diagnosed late.
Never shave-biopsy a suspected melanoma: a partial sample makes Breslow thickness unmeasurable. Excise the whole lesion with a narrow margin.
Fitzpatrick's Dermatology, 9th ed. (McGraw Hill, 2019); Bailey & Love's Short Practice of Surgery, 28th ed. (CRC Press, 2023).