Large congenital melanocytic nevus with metastatic melanoma with a probable primary in the lung.

Large congenital melanocytic nevi (>20 cm in greatest diameter) are very rare and are seen in approximately 1 in 20,000 newborns. The major risk these patients face is the development of neurocutaneous melanosis or malignant melanoma. We report a rare case of large congenital melanocytic nevus with metastatic melanoma in a 40-year-old woman. In this case, though the primary was not established with certainty, on the basis of clinical course and radiological evaluation of various organs, we presume that the primary could be in the lung.