Completely regressed primary cutaneous melanoma - difficulties in diagnosis and classification.

Complete regression of primary cutaneous melanoma is a very rare phenomenon. Only 49 cases of well-documented completely regressed primary cutaneous melanoma have been reported to date. The clinical picture and histological findings may vary considerably. The presence of regional lymphadenopathy represents a necessary requisite for the diagnosis of completely regressed primary cutaneous melanoma. However, some cases lie outside these criteria and are difficult to diagnose and classify. Moreover, completely regressed melanoma is not specifically referred to in the current AJCC (American Joint Commission on Cancer) melanoma staging system. We report three cases of completely regressed primary cutaneous melanoma. One of the cases presented with unquestionable clinical and histopathological findings of completely regressed primary cutaneous melanoma, but without concomitant regional lymph node metastasis. As expected, this patient eventually developed nodal metastatic disease. An extraordinary case of a completely regressed melanoma that appeared in association with a congenital melanocytic nevus is also documented. This case revealed a unique type of regression that affected only the melanoma. The nevus was left undisturbed by the immunological response.