[Oncocytic papillary renal cell carcinoma: a clinicopathological analysis of nineteen cases].

Objective: To investigate the clinicopathological characteristics, immunophenotype, and molecular signatures of oncocytic papillary renal cell carcinoma (OPRCC), and to compare these findings with those in type 1 papillary renal cell carcinoma (PRCC 1). Methods: The clinicopathologic data of 19 patients with OPRCC from the Affiliated Hospital of Qingdao University (16 patients) and the 971 Hospital of People's Liberation Army Navy (3 patients) from October 2003 to February 2021 were collected. Histologic, immunohistochemical (IHC) and molecular analyses, together with a control group of 15 cases of PRCC I diagnosed in the same period, were assessed. Results: The cohort included 15 males and 4 females, with a median age of 61 years (range, 47-78 years). In 13 patients the tumors were found at physical examination; four presented with painless gross hematuria and two with low back pain. As for the pathologic stage, 14 patients were pT1, one patient was pT2a, three patients were pT3a and one patient was pT4. The tumor size ranged from 1.7-14.0 cm, with clear boundary and soft texture. The cut surface was grayish-yellow and grayish-red. Microscopically, the tumor cells were mainly arranged in papillary (10%-100%) and acinar (tubular) patterns, with strongly eosinophilic cytoplasm, round or irregular nuclei, and prominent nucleoli (WHO/ISUP grade Ⅲ). Two cases showed sarcomatoid differentiation. Stromal foamy macrophages were visible in all cases. IHC staining showed diffuse strong positivity for AMACR in all cases. RCC (18/19), CD10 (17/19), vimentin (16/19) and PAX8 (17/19) were positive in most tumors. CK7 was expressed in about 50% of cases. Fluorescence in situ hybridization identified trisomy 7 in eight patients, trisomy 17 in seven patients, and the two aberrations occurred simultaneously in seven cases. Eight of 13 men had Y chromosome deletion. All patients were followed up for 8-120 months. Three patients died of metastases at 8, 62 and 82 months postoperatively, respectively, and one patient relapsed 36 months after surgery. Compared with PRCC1, OPRCC tended to have higher nuclear grade, and stromal foam cell aggregation was more commonly found (P<0.05). The expression of CD10 and EMA were different (P<0.01). There was no significant difference in the survival rate between the two groups (P=0.239). Conclusions: OPRCC has unique morphologic features, and its immunophenotype overlaps but differs from PRCC1. The molecular results support that it belongs to a morphologic variation of PRCC. This tumor has similar biologic behavior to PRCC1, and has a poor prognosis when sarcomatoid differentiation occurs.