[Collecting duct carcinoma associated with renal stones]

Collecting duct carcinoma is an extremely rare disease, representing less than 1% of all renal tumours. The authors report the case of a 72-year-old patient presenting with right low back pain associated with episodes of total macroscopic haematuria. Imaging showed a heterogeneous mass in the upper pole of the right kidney associated with pyelocaliceal stones. Multiple secondary lesions were observed in the liver. Macroscopically, the mid-renal tumour was 7.5 cm in diameter surrounding the stone-containing pyelocaliceal cavities. This tumour had spread to the cortex and invaded the perirenal fat. Histologically, the tumour was composed of ducts lined by cells with a hobnail appearance in an abundant desmoplastic and neutrophil-rich inflammatory stroma. Immunohistochemistry showed very intense labelling of tumour cells with cytokeratins: KL1, 7, 19, and 34_E12 and slightly less intense labelling with UER, Vimentin, EMA, and BNH9, while cytokeratin 20 was negative. The diagnosis of Fuhrman grade 3 collecting duct carcinoma associated with renal stones and liver metastases was adopted. The patient died postoperatively. The main differential diagnosis was urothelial carcinoma with a glandular component. In the present case, the diagnosis was made more difficult by the concomitant presence of renal stones. The diagnosis was established by histology and immunohistochemistry.