Solitary melanoma confined to the dermal and/or subcutaneous tissue - Evidence for revisiting the staging classification

Background: Several patients presented with a single focus of presumed cuta neous metastatic melanoma with an unknown primary tumor based on clinical a nd histologic staging criteria of the American Joint Committee on Cancer (A JCC). This population is classified as having stage IV disease by the curre nt AJCC staging system, which carries a dismal prognosis (5%-18% 5-year sur vival). Our clinical observation was that these patients had a higher survi val rate than would be expected for stage IV disease. We believe this popul ation represents a subgroup of primary dermal- and/or subcutaneously-derive d melanoma that simulates cutaneous metastatic melanoma in histologic and c linical presentation but may differ in behavior. Observations: The database records of 1800 patients from the University of Michigan Melanoma Clinic, Ann Arbor, were retrospectively reviewed to ident ify the prevalence and survival for patients diagnosed with a single focus of presumed metastatic melanoma to the skin based on accepted histologic an d clinical parameters. The prevalence of this population was 0.61% (11 of 1 800 patients). The Kaplan-Meier 8-year survival estimate was 83% (95% confi dence interval, 58%-100%). Conclusions: By AJCC convention, these cases are classified as stage IV met astatic disease. Our data suggest that these presumed metastatic tumors do not behave like stage IV metastatic disease to the skin via lymphatic or he matogenous spread from an unknown primary site; rather, they are behaving l ike primary tumors originating in the dermal and/or subcutaneous tissue.