Stage I melanoma of the skin: Evaluation of prognosis according to histologic characteristics

The prognosis for Stage I melanoma of the skin was evaluated on the basis of histologic characteristics of 699 primary tumors collected by the W.H.O. Melanoma Group from September 1967 to September 1975. Variables considered were maximum tumor thickness, levels of invasion, histologic type, number of mitoses, cell type, growth pattern, inflammatory reaction, angioinvasion, ulceration. When considered as single factors, these criteria, but cell type and inflammatory reaction, significantly affected survival (P < 0.05). However, when each criterion was adjusted by maximum tumor thickness, the number of mitoses and ulceration only were found to be still significant. The type of cells, which is not significant by itself (P = 0.92), becomes significant (P = 0.02) when adjusted by maximum thickness. The most important prognostic factor was maximum tumor thickness (P = 10−9). Using this criterion this series was divided into three groups: (1) “good prognosis” with maximum thickness not exceeding 2 mm and a five‐year survival rate of over 80%; (2) “intermediate prognosis” with maximum thickness between 2.01–4.00 mm and a five‐year survival rate between 50 and 80%; (3) “poor prognosis” with maximum thickness greater than 4.01 mm and five‐year survival rate of under 50%. All other prognostic criteria were evaluated within each group and it was found that the “intermediate prognosis” group cannot be divided into subgroups with different survival. The best survival was observed in patients with primary tumor not thicker than 2.00 mm with no ulceration (P = 0.01) or with spindle cells (P = 0.03); the worse survival was observed in patients with primary melanoma thicker than 4 with ulceration (P = 0.04) or with more than one mitosis per high power field (P = 0.04).