Tubulocystic carcinoma of the kidney with poorly differentiated foci: a series of 3 cases with fluorescence in situ hybridization analysis.

We identified 3 consult cases of tubulocystic renal cell carcinoma with poorly differentiated areas. Two lesions measuring 9.5 and 3.8 cm were described as partly solid and cystic. One case was grossly a 14.0-cm cyst with a granular lining. Microscopically, all had classic areas of circumscribed tubulocystic renal cell carcinoma occupying 30%, 80%, and 90% of the tumor; 2 cases had small components of papillary renal cell carcinoma, and 1 case had a central large cystic component. In 2 cases, proliferations of small tubules infiltrated away from the main mass with typical features of collecting duct carcinoma. In the third case, a focus of poorly differentiated carcinoma was seen adjacent to the tubulocystic renal cell carcinoma. In 2 cases, tumor invaded perirenal tissue. The third case was organ confined with vascular invasion. One patient died 9 months postoperatively with metastases to the abdominal wall and femur. The second case developed a recurrence in the renal bed 3 years postoperatively. The third patient was lost to follow-up. Fluorescence in situ hybridization studies results showed some features overlapping with papillary renal cell carcinoma in both the tubulocystic and collecting duct-like components and with 1 exception showed identical cytogenetic findings between the 2 components. Morphologically, in 2 cases, the collecting duct-like areas were also indistinguishable from collecting duct carcinoma suggesting a relationship between the 2 entities. This is the first series and only the second report of tubulocystic renal cell carcinoma with poorly differentiated components and documents the increased the risk of aggressive behavior above that of usual tubulocystic renal cell carcinoma.