De-Differentiated Metastatic Melanoma: A Diagnostic Challenge

Abstract Introduction/Objective Melanoma is one of the common malignant neoplasms with several histological appearances. Its diagnosis is usually based on histomorphologic findings and immunohistochemistry (IHC). De-differentiated melanoma (DM) is a special form of malignant melanoma with different histo-morphologic and immunohistochemical characteristics than conventional malignant melanomas. It has a worse prognosis and can impose a diagnostic challenge. Methods/Case Report A 62-year-old male previously had melanoma on his chest, which was surgically removed with negative margins and no involvement of nearby sentinel lymph nodes. The patient presented two months later with a rapidly enlarging mass in the right axillary region. Subsequent lymph node dissection revealed several nodes, the largest measuring 14 cm with extensive necrosis. Microscopic examination of the largest mass revealed clusters of irregularly shaped cells displaying marked nuclear abnormalities, prominent nucleoli, and heightened mitotic activity. Immunohistochemical analysis of this mass showed negative results for SOX-10, HMB45, Melan-A, S100 protein, CAM5.2, BRAF, and myogenin. Conversely, the remaining lymph nodes exhibited typical signs of melanoma metastasis, expressing relevant melanoma markers. Given the patient’s history of melanoma and the presence of metastatic melanoma in nearby lymph nodes, the histological and immunohistochemical findings support the diagnosis of dedifferentiated cutaneous metastatic melanoma. Results (if a Case Study enter NA) N/A Conclusion The distinctive appearance and lack of typical markers in this type of melanoma pose considerable difficulties in distinguishing it from other malignancies like poorly differentiated carcinomas and high-grade sarcomas. Furthermore, dedifferentiated melanoma tends to be highly aggressive, often resisting standard and immunological treatments. Therefore, comprehensive clinical and histomorphological assessments are crucial for accurately diagnosing these complex and challenging cases.