PROGNOSTIC FACTORS IN THIN CUTANEOUS MALIGNANT-MELANOMA

Background. Thin melanomas can metastasize and be lethal. The predicti ve importance of tumor thickness in thin melanomas and the specific fe atures identifying the patients at risk have not been investigated ful ly. Methods. Prognostic factors were analyzed in 585 patients with cli nical Stage I invasive cutaneous malignant melanoma with a thickness o f less than or equal to 0.8 mm. The patients were included in a popula tion-based cancer registry in Stockholm county during 1976-1987. They constituted about 64% of all patients with thin melanomas who were dia gnosed in the region during the study period. Information was availabl e on age, sex, anatomic site of the tumor, histologic type of melanoma , level of invasion, tumor thickness, and tumor regression. In a Cox r egression analysis, the prognostic importance of each factor was studi ed. By a case-control technique with individual matching for the ident ified independent predictors of recurrence, the additional prognostic information given by type and grade of inflammatory response, presence of vertical growth phase, mitotic rate/mm2, and histologic ulceration of the tumor was assessed. Results. After a median follow-up time of 50 months, recurrent disease developed in 26 patients (4%). There was no difference in recurrence rate between patients treated with narrow (1-2 cm) or wide (5 cm) excision. Anatomic site, tumor thickness, leve l of invasion, and tumor regression were found to be independent progn ostic factors in the multivariate analysis. In the case-control study, only grade of inflammatory reaction added significant prognostic info rmation. No subgroup could be identified that was without risk of recu rrent disease.Conclusions. Thin melanomas do not seem to constitute a separate form of melanoma, but compose one end of a continuous spectru m of biologic behavior.