Unusual variants of melanoma: fact or fiction?

Evidence is reviewed separating unusual variants of melanoma from the large group of superficial spreading and nodular (SSM/NOD) histogenetic types. These include (1) the relationship of moles to melanoma of the SSM/ NOD types not found in melanoma arising in lentigo maligna (LMM), desmoplastic neurotrophic melanoma (DNM), mucosal lentiginous melanoma (MLM), or acral lentiginous melanoma (ALM); (2) the strong sunlight association in lentigo maligna (LM) and LMM not always present in SSM/NOD and not likely at all in acral or mucosal lesions (ALM, MLM); (3) epidemiological differences of age, race, and prognosis among the various subtypes; and (4) analogies to neoplasms in other organ systems. These data justify the following conclusions: (1) Variants of melanoma exist as in other neoplasms. (2) They are of epidemiological and therapeutic importance. (3) Until further data are available or networked, data base analysis should use microstage measurements in the common forms of SSM and NOD only, and approach the unusual variants separately and cautiously.