Clear cell renal cell carcinoma presenting as a single cutaneous metastasis

Renal cell carcinoma (RCC) is the most common kidney tumor in adults, accounting for 2% of all cancers worldwide. It is two times more frequent in men than in women and it can metastasize to the lungs, liver, bones and brain. Skin metastases are unusual. A 79-year-old male with no personal history of malignancy, presents to the Department of Plastic Surgery for excision of a 36/32/14 mm ulcerated tumoral mass located in the right parietal area. Microscopic examination revealed a well-defined multinodular tumor located in the deep dermis, composed of a mostly solid and partially discohesive proliferation of cells featuring clear or granular-eosinophilic cytoplasm and vesicular nuclei with prominent nucleoli, lacking marked atypia. Mitotic rate varied from 2-3 to 12 mitoses per 10HPF. Focal areas of haemorrhage and necrotic debris as well as brisk lymphocytic infiltration were easily identifiable. The expansive and non-infiltrative pattern of growth supported the hypothesis of a metastatic tumor. The scarcity of clinical data and absence of a highly suggestive histopathological aspect, led to multiple differential diagnoses, including: large cell lymphoma, metastatic melanoma and metastatic carcinoma. Immunohistochemical stainings eventually confirmed the diagnosis of cutaneous metastasis of clear cell renal cell carcinoma (CD10+, PAX8+, Vimentin+) and excluded all other differentials (LCA-, Melan A-, AE1/AE3-, CK5/6-). Cutaneous metastases of RCC in the head and neck area are extremely unusual, given the distance from the anatomical site of the primary tumor. This case highlights the importance of careful clinical inspection of the skin in patients with internal organ malignancy.