Typing of renal tumors by morphological and immunocytochemical evaluation of fine needle aspirates.

Image-guided fine needle aspiration biopsy (FNAB) of renal masses can accurately evaluate malignancy. Adjunct methods are needed for accurate typing of renal cell carcinomas (RCC) and benign neoplasms. Cytopathological diagnoses of 79 routine ultrasound-guided FNAB of renal lesions were compared to consequent histological diagnosis and size of tumors. Cytology samples were sufficient for immunocytochemical subtyping in 43 cases (54.4%). The median tumor size was 2.8 cm, with 57 cases (76%) smaller than or equal to 4 cm. When a panel of immunocytochemical stainings (vimentin, CK7, CD117, P504S) was applied, accurate diagnoses were obtained in 11/12 (91.7%) of clear cell RCC (CRCC), 14/17 (82.3%) of papillary RCC (PRCC) and 5/7 (71.4%) of chromophobe RCC (ChRCC), respectively. Substantial cell pleomorphism with unusual immunostainings led to erroneous diagnosis of pheochromocytoma in CRCC with eosinophilic cytoplasm. Only 30% of CRCC were correctly diagnosed in the group without immunostaining, seven were suspicious for CRCC, and the remainder had unrepresentative material for CRCC. Cytopathological diagnoses were less accurate in oncocytomas (n=11), regardless of immunocytochemical staining. Cystic nephromas (n=2) and MEST (n=1) were overdiagnosed as suspicious and positive for PRCC, respectively, with immunocytochemical staining not assisting in correct diagnosis. RCC can be accurately typed as CRCC, PRCC or ChRCC in fine needle aspirates in a routine clinical setting if the cellular material is sufficient and a panel of antibodies is used (vimentin, CK7, P504S, CD117). The classification of oncocytomas and cystic nephromas is not reliable since atypical morphology and immunocytochemical reactions overlap with RCC.