Thin Cutaneous Malignant Melanomas (<= 1.5 mm) - Identification of risk factors indicative of progression

BACKGROUND, Although thin cutaneous melanomas generally have a favorable pr ognosis, in some cases they may undergo progression. The current study was undertaken to identify variables that may predict a more aggressive clinica l outcome in these patients. In addition to classic clinicopathologic featu res, the authors tested the prognostic impact of three new morphometric qua ntitative parameters: 1) tumor thickness plus regression thickness (T+R), 2 ) percentage of skin thickness infiltrated by tumor cells (T/S ratio), and 3) percentage of skin thickness infiltrated by tumor cells and regression ( [T+R]/S ratio). METHODS. The authors retrospectively evaluated 287 patients with invasive c utaneous melanoma less than or equal to 1.5 mm in thickness. Disease free s urvival rates (Kaplan-Meier method) were compared by using the log rank tes t. A multivariate analysis (Cox proportional hazards model) was used to det ermine the independent effect of each variable on progression. Progression was defined as any documented cutaneous local and/or distant metastasis. RESULTS, Thirty-two of the 287 patients (11.1%) underwent disease progressi on. The overall 5-year and 10-year disease free survival rates were 89.3% a nd 84.6%, respectively. In the univariate analysis, the following factors w ere found to be significant predictors of progression: male gender (P = 0.0 1), acral-lentiginous histotype (P = 0.02), tumor thickness (P = 0.005), TR (P = 0.001), T/S ratio greater than or equal to 50% (P = 0.031, (T+R)/S r atio greater than or equal to 50% (P = 0.006), vertical growth phase (P = 0 .04), and absence of inflammatory response (P < 0.0001). Conversely, age, s ite, and Clark's level did not affect the risk of recurrences and/or metast ases significantly. In the multivariate analysis, only T+R (P = 0.009) and inflammatory response (P < 0.0001) were found to be independent predictors of progression. Five-year disease free survival rates according to presence versus absence of inflammatory response were 93.4% and 63.8%, respectively (P < 0.0001). CONCLUSIONS. In the current study, peritumoral and intratumoral inflammator y infiltrate and T+R were found to be strong independent predictors of prog ression in thin cutaneous melanomas. Cancer 1999;85:1067-76, (C) 1999 Ameri can Cancer Society.