Fine-needle aspiration biopsy of chromophobe renal cell carcinoma and oncocytoma: Comparison of cytomorphologic features

BACKGROUND. Chromophobe renal cell carcinoma (ChRCC) is a distinct tumor with a prognosis intermediate between renal oncocytoma (RO) and clear cell renal cell carcinoma. To our knowledge the cytologic features of only a limited number of ChRCC have been described to date. A retrospective review of the cytomorphologic features of ChRCC and a comparison with RO was performed. METHODS. Fine-needle aspiration biopsies (FNABs) of six cases of histopathologically proven ChRCC were reviewed. The material examined was comprised of smears, cytospins, Thin Prep(®) Pap Test(TM) preparations, and cell block sections stained with Diff-Quik(®), Papanicolaou, and hematoxylin and eosin. Six FNABs of ROs were examined similarly. The cytomorphology of each tumor was studied and particular attention was paid to features differentiating the two entities. RESULTS. The characteristic cytomorphologic features of ChRCC (present in all cases) included round/oval, occasionally polygonal, moderately pleomorphic large cells present singly and in small clusters. The abundant cytoplasm was variegated, ranging from dense to flocculent to vacuolated, with prominent cytoplasmic membranes. The nuclei were large and hyperchromatic, with nuclear membrane irregularities and grooves present at least focally. Frequent binucleation was observed. Small nucleoli were present in many cells, but rarely prominent. In contrast, RO showed large cells with homogenous granular cytoplasm. The nuclei showed minimal to no nuclear membrane irregularities, tiny nucleoli, mild pleomorphism, and only an occasional large, more hyperchromatic nucleus was observed. CONCLUSIONS. ChRCC has a distinct combination of cytomorphologic features. Careful attention to cytoplasmic and nuclear features allows for the distinction between ChRCC and RO in cytologic preparations.