Clear Cell Renal Cell Carcinoma with Focal Psammomatous Calcifications: A Rare Occurrence Mimicking Translocation Carcinoma.

Abstract

Renal cell carcinoma (RCC) with clear cells and psammoma-like calcifications would often raise suspicion for MITF family translocation RCC. However, we have rarely encountered tumors consistent with clear cell RCC that contain focal psammomatous calcifications. We identified clear cell RCCs with psammomatous calcifications from multiple institutions and performed immunohistochemistry and fluorescence and RNA in situ hybridization (FISH and RNA ISH). Twenty-one tumors were identified: 12 men, 9 women, ages 45 to 83 years. Tumor size was 2.3 to 14.0 cm (median 6.75 cm). Nucleolar grade was 3 (n=14), 2 (n=4), or 4 (n=3). In addition to clear cell pattern, morphology included eosinophilic (n=12), syncytial giant cell (n=4), rhabdoid (n=2), branched glandular (n=1), early spindle cell (n=1), and poorly differentiated components (n=1). Labeling for CA9 was usually 80-100% of the tumor cells (n=17/21) but was sometimes decreased in areas of eosinophilic cells (n=4). All (19/19) were positive for CD10. Most (19/20) were positive for AMACR (variable staining, 20-100%). Staining was negative for keratin 7, although 4 showed rare positive cells (4/20). Results were negative for cathepsin K (0/19), melan A (0/17), HMB45 (0/17), TFE3 (0/5), TRIM63 RNA-ISH (0/13), and TFE3 (0/19) and TFEB rearrangements (0/12). Seven of 19 (37%) showed chromosome 3p deletion. One (1/19) showed trisomy 7 and 17 without papillary features. Psammomatous calcifications in RCC with a clear cell pattern suggests a diagnosis of MITF family translocation RCC; however, psammomatous calcifications can rarely be found in true clear cell RCC.