Tubulocystic renal cell carcinoma with poorly differentiated foci is indicative of aggressive behavior: clinicopathologic study of two cases and review of the literature.

Tubulocystic renal cell carcinoma (TCRCC) is a rare, recently characterized RCC subtype with distinctive clinicopathologic and genetic characterizations as well as typical behaviors in an indolent fashion. However, sporadic case reports in the literature have indicated that TCRCC with sarcomatoid differentiation or poorly differentiated (PD) foci could behave aggressively. Herein, we reported two cases of TCRCC with PD foci indentified from our consultative service. Both patients were male and aged 66 y and 47 y, respectively. The first patient experienced radical nephrectomy while the other was treated by partial nephrectomy. Macroscopically, both tumors were described as partly cystic and solid with the greatest diameter measuring of 12-cm and 4.5-cm, respectively. Histologically, both lesions had classic areas of TCRCC occupying most part of the tumor with small papillary RCC component. In case one, PD foci were scatteredly distributed and mixed with TCRCC and papillary RCC components, while in the other case the PD foci were adjacent to the areas of TCRCC. In both tumors, the PD foci were composed of irregular, often angulated, small tubules lined by atypical eosinophilic cells and surrounded by desmoplastic stroma, resembling collecting duct carcinoma. Immunohistochemistry, in both tumors, both TCRCC component and PD foci showed the similar immunoprofiles, i.e., labeling strongly and diffusely with PAX8, AMACR and Vimentin, and focally with CK34βE12 but not with renal cell carcinoma marker or P63. In case one, the tumor invaded extensively into the adjacent renal parenchyma and focally into both renal sinusal and perirenal adipose tissues. The patient had metastasis in the pelvic cavity at the time of diagnosis and succumbed to the disease without further treatment 3 months later. The other case was organ confined but with focal positive renal parenchymal margin. The patient subsequently underwent radical nephrectomy and was in a good status without evidence of tumor recurrence or metastasis at a follow-up of 8 months.