Ancillary studies in fine needle aspiration of the kidney

An increasing number of renal cell carcinomas (RCCs) require ancillary studies for diagnosis. The majority of renal fine needle aspirates do not require ancillary studies. Among the most common useful stains are cytokeratin 7 (separating clear cell RCC [negative] from papillary RCC, clear cell papillary RCC, and multilocular cystic RCC [positive] as well as separating chromophobe RCC [diffusely positive] from oncocytoma [focally positive/negative]) and CD117 (separating chromophobe RCC and oncocytoma [positive] from granular variants of clear cell RCC [negative]). CD68 and keratin are helpful in distinguishing RCC from xanthogranulomatous pyelonephritis. HMB45 is useful in recognizing scant aspirates of angiomyolipoma. Less common subtypes of RCC may benefit from the use of more specialized ancillary studies (succinate dehydrogenase B, fumarate hydratase, tumor suppressor gene INI, OCT3/4). While the majority of renal fine needle aspirates can be accurately diagnosed based on morphology alone, improved subtyping and accuracy can be achieved with the use of immunohistochemical and molecular studies. Cancer Cytopathol 2018;000:000-000. © 2018 American Cancer Society.