Fig. 3

Gross and microscopic examination of the metastatic lymph node metastasis. a On gross findings of the surgical specimen from the inguinal to scrotal and femoral mass, the huge, relatively well-demarcated and multi-nodular tumor, measuring approximately 8 × 6 cm, showed gray-whitish to yellow-whitish cut surfaces with hemorrhagic and yellowish necrotic foci. Bar  1 cm. b Microscopically, this inguinal tumor consisted of a diffuse proliferation of markedly atypical large cells, appearing predominantly as single cells (inset), involving and erasing the remarkably enlarged pre-existing lymph node tissue, partly surrounded by fibrous capsule (arrows). Bar  1000 μm. c On high-power view, these tumor cells contained hyperchromatic, pleomorphic mono- to multi-nuclei, and abundant eosinophilic to sometimes clear cytoplasm, admixed with a number of lymphocytes. Additionally, the large tumor cells occasionally had melanin pigments in the cytoplasm (left) and often showed autophagy (right). Bar  50 μm. d In immunohistochemistry, these malignant cells were specifically positive for melanocytic markers, such as HMB45 (left) and Melan A (right). Bar  100 μm