The classification of malignant melanoma and its histologic reporting

Abstract

Apart from the rare malignant melanomas occurring in blue nevi, primary cutaneous malignant melanoma arises in 1 of 3 ways, regardless of the presence or absence of a pre‐existing nevus. These three types have been designated: 1. Malignant melanoma, invasive, with adjacent intra‐epidermal component of Hutchinson's melanotic freckle type; 2. Malignant melanoma, invasive, with adjacent intra‐epidermal component of superficial spreading type; and 3. Malignant melanoma, invasive, without adjacent intra‐epidermal component. Occasionally, both clinically and histologically, there may be difficulty in deciding whether a malignant melanoma belongs to category 1 or 2, but, in the majority of cases, these 2 types can be quite readily distinguished. In addition to recording the histogenetic mode of development of a malignant melanoma, a histologic system of reporting is recommended which includes mitotic activity, levels of invasion, and vascular involvement. There are other parameters such as the cell type, pigmentation, lymphocytic infiltrates, evidence of spontaneous regression, associated nevi, and solar changes in the dermis, all of which are of unknown significance. The recording of these features, which are clearly of interest for research purposes, is left to individual discretion. It is emphasized that all the usual macroscopic descriptions and measurements should continue to be recorded.

Lentiginous melanoma: a histologic pattern of melanoma to be distinguished from lentiginous nevus

“…However, our cases were characterized by the confluent growth of atypical melanocytes spanning the entire lesion, similar to the proliferation seen in melanomas with a lentiginous junctional proliferation (lentigo maligna type, acral lentiginous type and mucosal lentiginous type). [3][4][5][6] In contrast to acral and mucosal lentiginous melanoma, our cases were all located on the head and neck, trunk and arm, and, histologically, there was preservation of the retiform epidermis and absence of prominent solar elastosis, in contrast to lentigo maligna. Immunohistochemical stains for Mitf and Mart-1 were useful in highlighting the extensive proliferation of basalar melanocytes as well as foci of pagetoid spread by melanocytes, not readily identifiable on the H-and E-stained sections.…”

Number of Nevi and Early-Life Ambient UV Exposure Are Associated with BRAF-Mutant Melanoma

“…Of the 285 cases, 16 were excluded after histopathologic review based on ineligible diagnoses (12 in situ, 1 mucosal and 1 metastatic melanoma, and 2 dysplastic nevi). Eligible cases (N = 269) were classified according to criteria proposed by Clark et al (25) and McGovern et al (26). Although in many cases, only biopsies of the melanoma were available for review, the biopsies typically contained the majority of the tumor, except for cases of lentigo maligna melanoma (LMM), but the findings were representative.…”

Tumor mitotic rate is a more powerful prognostic indicator than ulceration in patients with primary cutaneous melanoma

“…This method of assessing TMR was adopted after 1982, upon the recommendation of the participants of the 1982 Pathology Workshop 7 which revised the 1972 Sydney Classification of Malignant Melanoma. 8 In this original classification, the number of mitoses in at least 10 high power fields (HPF) over the entire lesion was counted and then expressed as the average number of mitoses/HPF. The 1982 Workshop participants considered that their revised method of assessing TMR, with results expressed as mitoses/mm 2 , would be independent of the particular microscope and magnification used and therefore results obtained in different parts of the world would become more comparable.…”