Multifocal or Metastatic B-RAF (V600E) Glomus Tumor in the Parotid and Neck: A Case Report Including Cytologic, Histologic, and Molecular Features

Abstract

Glomus tumor is a perivascular mesenchymal neoplasm that usually occurs as a solitary painful lesion of the distal extremities. It can also rarely occur in other anatomic locations, for example, the nasal cavity, trachea, stomach, and kidney. Although most tumors are benign, metastasis occurs in a small subset. Criteria for aggressive behavior remain incompletely defined, and the issue of defining metastasis is complicated by the occurrence of multifocal tumors. Here, we report a case of a multifocal glomus tumor involving the parotid gland (2 cm), ipsilateral sternocleidomastoid-clavicular soft tissue (1.5 cm), and ipsilateral subcutaneous tissue overlying the mastoid process (<4 mm) in a young man in his mid-20s. All 3 lesions were identical histologically, with typical features of an otherwise benign glomus tumor with uniform diploid-appearing nuclei and no mitotic activity. Very focal infiltrative growth was present. A prominent hemangiopericytoma pattern was present throughout, but no vascular invasion outside the nodules was identified. Molecular genomic analysis revealed an identical BRAF V600E point mutation in all 3 tumors in a wild-type BRAF somatic background, with similar patterns of genomic gains in 3 loci, consistent with a clonal origin. Criteria for predicting the behavior of glomus tumor are reviewed.