[Clinicopathological features of hybrid oncocytic/chromophobe renal cell tumor].

To investigate the clinicopathological features and immunohistochemical phenotypes of hybrid oncocytic/chromophobe tumor (HOCT) of the kidney and its associations with renal oncocytoma (RO) and eosinophilic chromophobe renal cell carcinoma (eChRCC). A total of 8 HOCT cases were collected from 2008 to 2019 at the Affiliated Hospital of Qingdao University (5 cases) and 971 Hospital of PLA Navy (3 cases), Qingdao, China for morphological studies, immunohistochemical staining and follow-up. The immunohistochemical results of HOCT were compared with those of 27 typical RO and 17 eChRCC. Among the 8 patients, 3 were male and 5 were female. Their ages ranged from 39 to 75 years (median: 56 years). All cases were sporadic. Seven patients were asymptomatic and one suffered from lumbago. During a mean follow-up of 37 months in 7 patients, none of them developed tumor recurrence or metastasis. Seven cases were solitary and one was multiple. The tumor size ranged from 1.4 to 5.7 cm (mean, 3.6 cm). The cut surface of the tumors was dark red or yellowish. Histologically, the tumors were well-defined. Six cases were directly adjacent to the surrounding renal tissue, 2 cases had pseudocapsule, 3 cases showed entrapped renal tubules at the edge of tumor tissue, and one circumscribed with focal infiltrating borders. There were two types of histological morphology: one type (4 cases) was composed of mixed areas of otherwise typical RO and areas resembling chromophobe renal cell carcinoma; another type (4 cases) showed the morphological characteristics of both RO and eChRCC. Three second-type tumors showed nest-like, trabecular, and solid growth patterns with conspicuous edematous stroma. The cell border was conspicuous and the cytoplasm showed an eosinophilic appearance. The nuclei were small and round with clear perinuclear halo. One tumor showed a multi-nodular and solid growth pattern, and the cytoplasm was eosinophilic, hypochromatic or transparent. The nuclei were small and round, and some of them had obvious perinuclear halo. Immunohistochemically, the tumor cells in all 8 cases were positive for Ksp-cad but negative for vimentin. CD117 was diffusely positive in 6/8 cases. CK7 staining showed patchy positivity in 6/8 cases. S-100A1, cyclin D1 and claudin7 showed variable positivity in 4/8, 6/8 and 5/8 cases, respectively, but the range and intensity were narrower and weaker than those in RO and eChRCC. HOCT is a low-grade eosinophilic renal tumor with morphological characteristics resembling RO and eChRCC. The combined application of immunohistochemical stains of CK7, CD117, Ksp-cad, cyclin D1, claudin7 and S-100A1 may play an auxiliary role in the differentiation of the three tumors. HOCT has a good prognosis after surgical resection and can be regarded as a tumor with uncertain malignant potential.