Regressed cutaneous malignant melanoma mimicking lymphoma: a potential diagnostic pitfall

We report 2 cases of partially regressed malignant melanoma in which the brisk lymphocytic response closely resembled mycosis fungoides in 1 case and nodular sclerosing Hodgkin lymphoma in the other. Striking epidermotropism was present in both cases. The lymphocytes were predominantly of T8 cytotoxic subtype, and oligoclonal T-cell expansion was detected in 1 of the cases. The scanty residual melanoma cells were highlighted with HMB45 and S100 protein. We highlight the features of regression in melanoma that may lead to an erroneous diagnosis of lymphoma and discuss the finding of oligoclonal T-cell expansion in regressed melanocytic lesions.