Clark level

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A measure of the depth of invasion of a malignant melanoma according to the layer of skin it has invaded into.

Clark's levels
Level Depth of Invasion
I All tumour cells are above the basement membrane. In situ melanoma by definition.
II The neoplastic cells have broken through the basement membrane and extended into the papillary dermis but have not gone to the reticular dermis. Allows for occasional cells or nests of tissue straying into the reticular dermis.
III Tumours cells at the interface between the papillary and reticular dermis.
IV Distinct invasion of tumour into the reticular dermis. Allows for isolated intrusion of cells between the collagen bundles of the upper reticular dermis.
V Invasion of neoplastic cells into the subcutaneous tissue.

Compared to the Breslow thickness, it may be less good at predicting prognosis,[1] but may be helpful in thin melanomas where Breslow thickness may be misleadingly optimistic.[2]

References