Malignant neurocristic hamartoma: a tumor distinct from conventional melanoma and malignant blue nevus.

Neurocristic hamartomas are rare pigmented lesions comprised of melanocytes, Schwann cells, and pigmented dendritic spindle cells that involve the skin and soft tissue. Malignant transformation can rarely arise within neurocristic hamartomas. Up to date, there has been only 1 series of 7 cases of malignant neurocristic hamartomas (MNHs), with 3 cases that developed metastases. We present the histology and clinical course of 3 additional cases of MNH, 2 of which were metastatic. CD117 was strongly positive in all cases with available archival materials--the tumors and background neurocristic hamartoma of 3 cases, and 1 lymph node metastasis; however, KIT sequencing for exons 11, 13, 17, and 18 was negative. Mutational analyses of recurrent mutations of 17 cancer genes, including BRAF and KIT, were also negative. Although our series is small, KIT overexpression in MNH does not seem to correlate with gene mutation. The lack of BRAF, NRAS, GNAQ, and KIT mutations seems to support the notion that MNH may be distinct from conventional melanoma and from other dermal melanomas, such as malignant blue nevi and melanoma arising in congenital nevi.