Cytogenetic and Immunohistochemical Study of 42 Pigmented Microcystic Chromophobe Renal Cell Carcinoma (PMChRCC)

Pigmented microcystic chromophobe renal cell carcinoma (PMChRCC) is a recently described morphologic variant of ChRCC. We have identified 42 cases in 40 patients in the last 24 years. We have investigated their clinical, morphologic, immunohistochemical, and cytogenetic features. Chromosomal abnormalities of chromosomes 7 and 17 were evaluated by automated dual-color silver-enhanced in situ hybridization on paraffin-embedded tissue. Chromosomal imbalance was defined on the basis of changes in both chromosomal index and signal distribution. The main age was 60.20 years, being 34 males and 6 women. The mean tumor diameter was 4.84 cm, with 39 intrarenal tumors. Grossly, the tumors were solid with a brown dark colored. Microscopically, tumors consisted of pale and eosinophilic cells arranged in microcysts or microalveolar in a cribriform pattern; there were microcalcifications and a dark brown pigment, mostly extracellular. One case showed sarcomatoid transformation. All tumors were positive for epithelial membrane antigen (EMA), Claudin 7, and E-cadherin. Monosomy of 7 and 17 chromosomes was present in 1/36 cases and 2/37 cases, respectively. Polysomy of chromosome 7 and 17 was found in 26/36 cases and in 4/37, respectively. With a median follow-up of 74.05 months, 37 patients were alive without disease and two were alive with disease progression. PMChRCCs expand the morphologic spectrum of the ChRCC with an unusual immunohistochemical profile. Cytogenetically, they showed monosomy to chromosome (CHR) 17 as other ChRCCs and polysomy of CHR 7 infrequent to ChRCCs. We present the probably largest series of PMCRCC, confirming their low aggressive behavior, with exceptional sarcomatoid transformation and distant metastases.