Loss of BAP1 protein expression in the first metastatic site predicts prognosis in patients with clear cell renal cell carcinoma.

OBJECTIVES: To investigate the intratumoral heterogeneity of BAP1 and PBRM1 expression at the primary site and metastatic sites and to evaluate whether BAP1 and PBRM1 expression in metastatic sites of clear cell renal cell carcinoma (ccRCC) has prognostic value.

METHODS AND MATERIALS: We collected paired samples from the primary site and the first metastatic site in 41 patients with ccRCC. Immunohistochemistry analyses were performed for the expression of BAP1 and PBRM1 proteins. We retrospectively analyzed the associations between the expression of BAP1 and PBRM1 and overall survival (OS).

RESULTS: The most common first metastatic sites were lung (68.3%) and lymph node (12.2%). BAP1 protein expression was negative in 8 (19.5%) primary sites and in 11 (26.8%) metastatic sites. PBRM1 protein expression was negative in 9 (22.0%) primary sites and in 11 (26.8%) metastatic sites. The incidences of intratumoral heterogeneity for BAP1 and PBRM1 protein expression in primary/metastatic sites were 9.8%/2.4% and 24.4%/7.3%, respectively. The concordance rates between primary and metastatic sites for BAP1 and PBRM1 protein expression were 82.9% and 63.4%, respectively. Median OS from the first occurrence of metastasis in patients with BAP1-positive and BAP1-negative metastatic sites were 97 months (95% CI: 58-136) and 51 months (95% CI: 13-82), respectively (P = 0.0077). Median OS in patients with PBRM1-positive and PBRM1-negative metastatic sites were 82 (95% CI: 42-97) and 120 (95% CI: 52-120) months, respectively (P = 0.25).

CONCLUSION: Intratumoral heterogeneity of BAP1 protein expression is more frequent in primary tumor than in metastatic sites. The loss of BAP1 protein expression in metastatic sites predicts poor prognosis in patients with ccRCC.