Hybrid chromophobe renal cell neoplasm.

Hybrid renal cell neoplasms (HRCNs) containing areas of tumor cells displaying cytological features of chromophobe renal cell carcinoma (CHRCC) and renal oncocytoma (RO) have been recently described in patients with renal oncocytosis and Birt-Hogg-Dube (BHD) syndrome (autosomal dominant genodermatosis). In this study, we identified cases of sporadic HRCN. We reviewed 425 consecutive renal cell carcinomas (RCC), 18 CHRCC, six HRCN, and 25 RO. Five HRCN were identified, including four from the group of RCC and two from RO. Patient age ranged from 40 to 68 years (mean age: 54 years), and the male:female ratio was 4:1. Tumors measured from 1.8 to 5 cm (mean diameter: 3.0 cm). Tumoral necrosis was not seen. Vascular invasion into medium-sized veins was identified in one HRCN. Chromophobe cells accounted for 20-80% of the tumors. Hale's colloidal stain showed weak to moderate diffuse cytoplasmic staining in scattered cells corresponding to those displaying routine staining features of chromophobe cells. Areas of oncocytic cells in studied tumors and control oncocytomas showed negative or focal cytoplasmic staining usually bordering extra- or intra-cytoplasmic lumina. Immunostaining for cytokeratin 7 and vimentin showed focal immunoreactivity in three cases and negative reactivity in all six cases, respectively. None of the study cases had microscopic RO, as commonly seen in renal oncocytosis, or were associated with BHD syndrome Sporadic HRCN accounted for 1% of RCC. They were of smaller size than RCC and were associated with a favorable prognosis.