Pigmented microcystic chromophobe renal cell carcinoma.

We report a case of a 60-year-old female with a pigmented microcystic chromophobe renal cell carcinoma (PMCRCC). The tumor was 4.5 cm in diameter, and was located in the right kidney. Grossly, on cross section, the tumor was light gray with multiple small brown to black pigmented foci up to 0.2 cm in diameter. Histologically, the tumor showed a microcystic arrangement with cribriform areas and formation of adenomatous structures. The microcystic and cribriform areas were composed of larger pale cells and smaller eosinophilic cells, with cytological features of conventional chromophobe renal cell carcinoma (CRCC). The cytological features of the cells within the adenomatous structures were different. These cells were mostly columnar with nuclei at the base, and had a variable amount of pale to eosinophilic cytoplasm. There were foci of ample brown pigmentation located in the cytoplasm of the tumor cells and extracellularly. In addition, microscopic calcifications were present. Immunohistochemically, the tumor cells were positive for EMA, E-cadherin, cytokeratin CAM5.2, and cytokeratin AE1/AE3. Cytokeratin 7 was positive only focally. S-100 protein, melan A, HMB 45, vimentin, and CD117 were negative. PMCRCC is a rare tumor. To the best of our knowledge, only one series containing 20 cases of this variant of CRCC has been described to date. The important feature is that PMCRCC seems to have a relatively benign biological behavior, and distant metastases and sarcomatoid transformation are absent.