Can Mutations in the BAP1 Gene be Detected by Immunohisto-chemistry in Hereditary Kidney Cancers?

Abstract

Background: Hereditary renal cell carcinoma (RCC) constitutes about 5% of all RCCs. The most common and well studied syndromes include, VHL, HLRCC, BHD, Familial Oncocytoma, RCC Papillary Type 1, TSC, RCC associated with Succinate dehydrogenase B (SHDB) mutations and others. Several genes, including VHL, MET, FLCN, FH and genes encoding the succinate dehydrogenase (SDH) subunits B/C/D have been identified as causative. However, the genetic basis of a significant percentage of familial RCC, some with clear cell morphology remain unknown. BAP1 (BRCA1 associated protein-1), a tumor suppressor gene that encodes a nuclear deubiquitinase, is inactivated in 15% of sporadic clear cell RCCs and its loss was associated with high tumor grade and poor prognosis. In this study, we investigated the possible role of this gene in the spectrum of RCC part of hereditary syndromes. Materials and Methods: To elucidate the role of BAP1 in all the spectrum of hereditary RCC, we studied by IHC a panel of RCCs which covers the spectrum of kidney cancers and included 10 VHL tumors, 6 HLRCCs, 8 chromophobe, 5 Hereditary Papillary Type 1, 6 Oncocytomas, 3 BHD (hybrid), and 24 sporadic clear cell RCCs. To analyze the BAP1 expression in these tumors, formalin fixed paraffin embedded (FFPE) tissues were immunostained with mouse monoclonal anti-human BAP1 antibody (Clone C-4, Santa Cruz). Results: We found that all the tumors except two showed positive nuclear staining for BAP1. The two negative cases that were negative for BAP1 were Clear cell type and belonged to two siblings. Molecular analysis in a prepublished study showed both patients harboring the p.L14H mutation. Conclusion: Our study supports the hypothesis that BAP1 mutations can play a role in hereditary syndromes predominantly in clear cell tumors. Staining for BAP1 should be done when there is no definite known mutation in a clear cell cancer but the patient gives history of familial kidney cancer. The two related patients who had similar mutations had aggressive, metastatic disease, which suggests that probably BAP1 does play a role in hereditary RCC clear cell type.