Can renal oncocytomas be distinguished from renal cell carcinoma on fine-needle aspiration specimens? A study of conventional smears in conjunction with ancillary studies.

Abstract

The reliability of using fine-needle aspiration (FNA) to distinguish renal oncocytoma (RO), a benign tumor, from renal cell carcinoma (RCC), which has eosinophilic granular cytoplasm, has been questionable. However, it is clinically significant, because radical nephrectomy may be avoided in patients with RO. The authors retrospectively studied the cytologic features and ancillary study findings of RO compared with findings in RCCs with eosinophilic granular cytoplasm to evaluate the reliability of FNA-based diagnosis of RO. The authors reviewed 19 tumors, including 11 ROs, three chromophobe RCCs (CRCCs), three granular variant RCCs (GRCCs), and two eosinophilic variant papillary RCCs (EPRCCs). Smears and cell blocks were prepared using either computed tomography-guided or ultrasound-guided FNA material. Surgical specimens were available for all tumors. Cytokeratin, vimentin, and Hale colloidal iron (HCI) stains were performed on all 19 tumors. Electron microscopy (EM) was available for six tumors. Although most tumors demonstrated their classic cytologic features, the specific diagnosis using conventional smears or even core biopsies was difficult in some tumors, especially ROs, due to the overlapping cytomorphology among these tumors. Cytologic material was obtained from 10 of 11 RO specimens. Of 10 ROs, 8 original FNA-based diagnoses were oncocytic neoplasm. Immunoperoxidase studies revealed that all tumors of each type were positive for cytokeratin, whereas only GRCCs and EPRCCs were positive for vimentin. The two vimentin negative neoplasms, RO and CRCC, could be distinguished by HCI stain, which showed diffuse or focal cytoplasmic positivity in CRCCs and apical/perinuclear staining (73%) or negative staining (27%) in ROs. Ultrastructurally, cytoplasm densely packed with mitochondria was characteristic for oncocytoma. This study demonstrated that ROs can be distinguished reliably from RCCs on the basis of cytologic morphology combined with ancillary studies, including immunostaining with cytokeratin and vimentin antibodies and HCI stain. EM provides additional information to confirm the diagnoses.