Metastatic malignant melanoma with Homer-Wright rosettes mimicking a neuroblastic tumor. An unusual morphological manifestation

Excerpt

Sir, malignant melanoma is considered "the great histologic mimic" since it may exhibit a wide variety of histological patterns, mimicking any kind of tumor including sarcomas, carcinomas, lymphomas, plasmacytomas, and germinal tumors. Real ganglioneuroblastic differentiation is an exceptional event that has only been described in one case of malignant melanoma [3]. We report a case of lymph-node metastatic malignant melanoma with extensive areas of a neuroblastic-like morphology characterized by melanin pigmented Homer-Wright rosettes but without evidence of ganglionary differentiation. The patient, a 61-year-old man visited the dermatologist because of a 3-month history of a progressively enlarging 1.8-cm pigmented skin nodule on his abdominal wall that occasionally presented spontaneous bleeding. He had no other symptoms and denied fever or weight loss. Complete surgical resection was performed. The histopathological study identified a classic superficial spreading malignant melanoma level IV of Clark with a Breslow thickness of 4.8 mm (Fig. 1). The patient remained well with no recurrence until 4 years later, when he developed a progressively enlarging axillary mass. An axillary lymph-node resection was performed and four lymph nodes were taken. Microscopically, one of these was entirely replaced by a malignant tumor composed of sheets of spindle and epithelioid cells arranged in a typical Homer-Wright rosette pattern (Fig. 2). The tumoral cells had large nuclei with pseudoinclusions, coarse chromatin and eosinophilic cytoplasm. The presence in these rosettes of a subtle brown cytoplasmic pigment (Fig. 2, inset), along with the patient's previous history, led to the diagnosis of metastatic malignant melanoma. Moreover, the tumor was inmunohistochemically positive for specific melanocytic markers such as S-100 protein (polyclonal, Dako, UK, 1:2000), HMB-45 (HMB-45, Biogenex, 1:10) and melan A (A103, Dako, UK, 1:10) and negative for neural/neuroendocrine antibodies including: synapthophysin (SY38, Dako, UK, 1:10), chromogranin (LKZH10, Biogenex, 1:50), neurofilament (ZF11, DAKO, UK, 1:25) and glial fibrillary acid protein (Polyclonal, Dako, UK 1:3000). The antigen retrieval was performed in all cases by heat (pressure cooker) in citrate buffer 10 mM pH 6, except for S-100 protein where protease XIV (Sigma) was used. The patient was treated with chemotherapy and 4 months later he developed lung and liver metastases, was not biopsied, and died of metastatic disease 4 years and 5 months after the initial diagnosis of primary cutaneous malignant melanoma.

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