Mucin-secreting clear cell renal cell carcinoma. A rare variant of conventional renal cell carcinoma.

We report herein one case of conventional renal cell carcinoma (RCC) producing extensive extracellular mucinous secretion in a 71-year-old man. To the best of our knowledge, the presence of mucinous secretion in this tumor has not been documented. Mucin production, despite its low frequency, can be considered an additional feature of conventional RCC. Therefore, clear cell RCC should be added to the list of parenchymal renal tumors that can show significant mucin secretion; and it should be included in the inventory of morphologic variations of this tumor, which may cause diagnostic difficulties. It is of primary importance to distinguish mucin-secreting clear cell RCC from the metastasis of a mucin-secreting tumor to conventional RCC. Presence of mucin in a clear cell carcinoma does not exclude a renal origin.