Histological characteristics of metastasizing thin melanomas: a case-control study of 43 cases.

Abstract

To study clinical and histological features associated with metastasizing thin melanomas (MTMs). Case-control study of clinicopathological features of patients with MTMs by a panel of 10 dermatopathologists. Members of the North American Melanoma Pathology Study Group selected the cases from the melanoma databases at 8 academic institutions. Forty-three patients with MTMs (<1 mm thick) and 42 control subjects without metastasis matched for age, sex, tumor site, and Breslow thickness. None. Clinical (age, sex, site of lesion, stage at diagnosis, metastasis site, disease-free survival, and outcome) and histological (Breslow thickness, Clark level, growth phase, regression, and inflammatory response) features of patients with MTMs vs controls. There was an overrepresentation of axial tumors among patients with MTMs. Extensive regression was present in 18 patients (42%) with MTM vs 2 matched control subjects (5%) (95% confidence interval, 21%-53%; P =.001). Other histological variables were not significantly different. Two patients had melanomas in situ with subsequent metastasis. Thin melanomas with extensive regression represent a group at higher risk for the development of metastasis. Furthermore, the risk of metastasis cannot be dismissed in cases of melanoma in situ.