Prognostic role of BAP1 in pT1 clear cell carcinoma in partial nephrectomy specimens

BAP1 is a gene situated on chromosome 3p in a region that can be modified in renal cell carcinomas (RCCs). Mutations that cause loss of expression of BAP1 frequently occur in primary clear cell renal carcinoma (ccRCC). In a previous work, we observed that loss of nuclear BAP1 expression was crucial in ccRCC progression; in the current study, we investigated BAP1 expression in a large series of small conventional ccRCCs treated with partial nephrectomy, to assess a possible role as biomarker and the prognostic value in terms of patients’ survival at long-term follow-up. One hundred sixty-two patients with single pT1 ccRCC were selected from those who underwent surgery at our Institute of Urology between 1987 and 2000. The features considered in this study were gender, age, tumor size, grade, incidence of metastasis, and patient-specific survival; they were correlated with immunohistochemical BAP1 nuclear expression in tumoral tissue. Median follow-up was 197.24 months (range 19 to 274); median survival was 125.34 months (range 5 to 274 months). None of our pT1 ccRCCs showed total loss of nuclear BAP1 staining; we found a significant negative correlation between nuclear BAP1 expression and tumor size and between nuclear BAP1 expression and grade. In small ccRCCs, nuclear BAP1 staining was not correlated with disease-specific 5-year survival.

Our data confirm the established role of BAP1 as a tumor suppressor protein. This is the first report where BAP1 has been studied in pT1 ccRCC tumors, but nuclear BAP1 expression cannot help identify patients having high-risk disease in these patients.