A prognostic model for clinical stage I melanoma of the trunk. Location near the midline is not an independent risk factor for recurrent disease.

Fifteen variables were studied for their usefulness in predicting recurrent disease in 254 patients with clinical stage I melanoma of the trunk. Thickness of the primary tumor correctly predicted outcome with an accuracy of 90 percent or greater in 176 patients with melanoma primaries with a thickness of less than 1.70 mm or 5.5 mm or greater. No other variables significantly increased predictive accuracy over these ranges of thickness. A Cox proportional hazards analysis of the remaining 78 patients with primary tumors 1.70 to 5.49 mm thick demonstrated that the following four variables functioned as independent risk factors for recurrent disease: (1) thickness of the primary tumor (p = 0.0005), (2) mitoses/mm2 greater than 6 (p = 0.006), (3) a nearly absent or minimal lymphocyte response at the base of the tumor (p = 0.009), and (4) location on the upper trunk (p = 0.03). Trunk lesions located near the midline did not have a worse prognosis than more lateral melanomas of similar thickness.