Melanoma
A malignant proliferation of melanocytes that, unlike a benign naevus, grows asymmetrically and eventually invades vertically into the dermis, and it is the depth of that invasion at diagnosis, the Breslow thickness, that is the single strongest predictor of survival.
First principles
Melanoma is a melanocyte that has escaped normal growth control
Melanocytes normally sit as a regulated, evenly-spaced population along the basal layer. Cumulative ultraviolet damage causes DNA mutations that let a melanocyte clone proliferate outside that control, first spreading sideways within the epidermis (radial growth phase) and, in more advanced lesions, downward into the dermis (vertical growth phase). Almost every clinical and prognostic feature of melanoma follows from where a given lesion sits on that radial-to-vertical progression.
Educational content pending clinical review. Not medical advice.