Collecting-duct carcinoma of the kidney with prominent signet ring cell features

Collecting-duct carcinomas (CDCs) comprise approximately 1% of renal epithelial malignancies. We report a case of collecting duct carcinoma with prominent signet ring cell features in a 60-year-old man. Grossly, the tumor measured 7.5 cm in greatest dimension, occupied the entire lower pole of the kidney, and was well-circumscribed. Microscopically, it displayed a predominant tubulopapillary pattern of growth with a desmoplastic stroma. The tumor tubules were lined by a single layer of cells with large, pleomorphic nuclei, some of which had a hobnail appearance. Large intracytoplasmic vacuoles with compression of nuclei (signet ring cells) were present throughout the tumor. Alcian blue, mucicarmine, and periodic acid-Schiff stains failed to identify intracellular mucin or glycogen in the signet ring cells. The tumor cells were immunohistochemically positive for cytokeratin (cytokeratin 7) and vimentin. To the best of our knowledge, this is the second reported case of renal CDC with prominent signet ring cell features.