Base of tongue metastasis of cutaneous malignant melanoma with rhabdoid and neuroendocrine features: Report of a rare case and review of the literature

Abstract

Metastatic malignant melanoma (MM) represents a highly aggressive cancer associated with overall poor prognosis. Various anatomic sites can be affected, including the oral cavity and the oropharynx. It may mimic other entities by assuming a variety of clinical appearances and exhibiting a plethora of microscopic variations. Herein, we present a case of a 63-year-old male with a MM metastasizing to the base of tongue, which developed 5 years after the original diagnosis and treatment of cutaneous MM of the chest and heralded its relapse; subsequently, neurological symptoms developed as a result of metastasis to the brain. Diagnostic challenges were encountered, as the tongue lesion clinically masqueraded as a pedunculated reactive lesion and microscopically displayed unusual rhabdoid and neuroendocrine features. Tumor cells expressed S-100, HMB-45, Melan-A, and SOX-10, while most cells with rhabdoid morphology were also positive for myogenin and Myo-D1. Chromogranin and synaptophysin positivity was further noticed in a subset of cells, suggestive of focal neuroendocrine differentiation. Molecular investigation revealed mutations for the BRAF V600E gene. Divergent differentiation of tumor cells may cause diagnostic pitfalls necessitating thorough immunohistochemical analysis. The presence of rhabdoid features and neuroendocrine differentiation are very uncommon, while their co-existence is extremely rare. Better characterization of such microscopic variations in MMs with evaluation of their potential biologic significance is warranted.

Keywords: Base of tongue; Malignant melanoma; Metastasis; Neuroendocrine differentiation; Rhabdoid features.

Fig. 1

Clinical examination. a and b) Exophytic, pedunculated, partially ulcerated, friable hemorrhagic mass of soft consistency involving the left base of tongue

Fig. 2

Gross examination. a) Partially ulcerated and somewhat lobulated mass of brownish color measuring 2.5 × 1.5 × 1.5 cm. b) Brown to tan cut surfaces of the solid tumor mass

Fig. 3

Histopathologic examination. a) Diffuse infiltration by malignant cells organized in solid sheets. b) Diffuse melanin pigmentation within the cytoplasm of tumor cells, which show predominant epithelioid features, pleomorphism, prominent eosinophilic nucleoli, and atypical mitotic activity. c and d) Large polygonal rhabdoid cells with eccentric nuclei and abundant eosinophilic cytoplasm forming nests. e) Clusters of small cells with neuroendocrine features. f) Absence of junctional activity. Hematoxylin and eosin, initial magnification 200x

Fig. 4

Immunohistochemical analysis. Diffuse and intense positivity of tumor cells for S-100 (a), HMB-45 (b), Melan-A (c), and SOX-10 (d). Cells with rhabdoid morphology expressed myogenin (e) and Myo-D1 (f). Focally, a minority of cells were positive for synaptophysin (g) and chromogranin (h), suggestive of neuroendocrine differentiation

Fig. 5

Complete healing with no evidence of any residual lesion in the left base of tongue