Natural history of cutaneous malignant melanoma

The rising incidence of cutaneous malignant melanoma with the consequent increase in mortality from melanoma has intensified efforts to understand the factors that initiate the malignant transformation of melanocytes and to define those tumor‐host interactions that play a relevant role in the clinical course of this disease. Increased exposure to solar radiation has been proposed as an explanation for the rising incidence of melanoma observed in light‐skinned races. Because of the low incidence of melanoma in darkly pigmented races and its tendency in these individuals to develop in relatively nonpigmented areas, such as the sole of the foot, it is postulated that melanin, in addition to its well‐known photoprotective effects, may protect against certain intrinsic carcinogenic agents. Developing cutaneous malignant melanomas progress through several cell types that have varying potentials for invasion and metastasis. This developmental process can be appreciated by examination of the various histologic types of melanomas. Early superficial spreading melanoma and lentigo maligna melanoma are characterized by cells that exhibit a prolonged intraepidermal growth phase, and most of these lesions can be diagnosed while they are still curable by simple surgical therapy. Subpopulations of more aggressive cells eventually develop, however. These cells also may characterize the initial stages of nodular melanoma in which the intraepidermal growth phase is absent and early invasion is common. Prognosis for survival depends on the depth of invasion of the primary tumor. Microstaging of the depth of invasion together with information as to mitotic index, sex, site, age, and histologic type will usually predict the natural history of the disease. With present‐day management, the overall long‐term, disease‐free survival rate of patients with cutaneous melanoma is 60–70% and compares favorably with that of the more common cancers. Résumé La fréquence croissante des mélanomes malins et l'augmentation de la mortalité ont stimulé les recherches qui étudient les facteurs de transformation maligne des mélanocytes et les interactions hôtetumeur qui jouent un rôle important dans l'évolution de cette maladie. On a suggéré que l'exposition aux rayons solaires expliquait l'augmentation de fréquence du mélanome dans les races à peau claire. Comme le mélanome est rare dans les races à peau foncée et qu'il apparait, chez ces individus, de préférence dans les zones non pigmentées, tel