Thin Melanomas: Predictive Lethal Characteristics from a 30-Year Clinical Experience

Objective: To guide treatment and clinical follow-up by defining the natural history of thin melanomas and identifying negative prognostic characteristics that may delineate high-risk patients. Summary Background Data: In following > 10,000 patients with cutaneous melanoma over the past 30 years, our institution has observed nodal or metastatic disease in approximately 15% of patients with a thin (<1 mm) primary lesion. Methods: A database query of patients with cutaneous melanoma returned 1158 patients with primary lesion ≤ 1 mm thick and who received their initial treatment at a single institution. Median follow-up was 11 years (range, 1 to 34 years). Patient and melanoma characteristics as well as outcomes were recorded and statistically analyzed. Results: 6.6% of patients had nodal or distant disease at presentation. Over time, an additional 9.4% developed metastases, including nodal and distal recurrences. Overall incidence of advanced disease was 15.3%. Univariate analysis identified male gender (P = 0.01), advanced age (>45 years; P = 0.05), and Breslow thickness (>0.75 mm; P = 0.008) as significant negative prognostic characteristics. Of patients with these 3 high-risk characteristics, 19.7% developed advanced disease (likelihood ratio 6.3; P = 0.007 versus nonhigh-risk patients). This group had more than twice the incidence of nodal recurrences. Patients with recurrence had significantly decreased 10-year survival (82% versus 45%; P < 0.0001). Surprisingly, neither ulceration nor Clark level predicted advanced disease. Conclusions: Thin melanomas are potentially lethal lesions. Long-term follow-up identified a high-risk population of older males with tumors between 0.75 mm and 1.0 mm whose risk of recurrent disease approaches 20%. Traditionally accepted negative prognostic factors such as ulceration and discordant Clark levels are not predictive for metastasis in this population. Given the poor prognosis associated with recurrent disease, we recommend close clinical evaluation and follow-up to maximize accurate staging and therapeutic options.