Melanocytomas of the central nervous system: a clinicopathological and molecular study

Abstract

Background: Melanocytomas of the Central Nervous System (CNS) are rare and benign lesions. These slow-growing tumours can behave aggressively, with local recurrence. Various genetic aberrations occur in malignant melanomas and raise possible new therapeutic options. However, little information is available regarding these characteristic genetic alterations in melanocytomas of the CNS. This study was designed to better understand the clinicopathological and molecular features of melanocytomas.

Materials and methods: Twenty cases of melanocytoma were studied by light microscopy, electron microscopy and immunohistochemistry. Clinical characteristics, therapeutic options and prognosis were analysed. BRAF, NRAS and KIT gene mutations were tested by direct DNA sequencing.

Results: Fourteen of twenty patients had intracranial tumours including one associated with naevus of Ota and six were spinal. Histologically, these tumours contain fusiform and epithelioid cells with little or no cellular pleomorphism and rare mitoses. Immunohistochemical and ultrastructural findings confirmed the origin of tumour cells as melanocytic. None of the melanocytomas harboured BRAF, NRAS and KIT mutations. Patients with complete resection had no tumour recurrence. Moreover, patients with incomplete tumour resection followed by radiotherapy showed a higher local control (LC) rate than incomplete resection alone (P < 0·05).

Conclusions: BRAF, NRAS and KIT mutations appear to be rare, if not completely absent in melanocytomas of the CNS. The complete resection of the tumour or incomplete resection followed by radiotherapy should be considered as better therapeutic options to reduce the tumour recurrence.

Keywords: BRAF; Central Nervous System; melanocytoma; mutation; prognosis; radiotherapy.