BAP1

Pathology

 Germline mutations in BAP1

• in melanocytic tumors
  • Germline mutations in BAP1 cause a familial tumor syndrome characterized by high penetrance for melanocytic tumors with distinct clinical and histologic features.
  • Melanocytic neoplasms in affected individuals harbored BRAF mutations, showed loss of BAP1 expression, and histologically resembled so-called "atypical Spitz tumors" (ASTs).
  • BRAF-mutated, BAP1-negative tumors are primarily located in the dermis and are composed entirely or predominantly of epithelioid melanocytes with abundant amphophilic cytoplasm and well-defined cytoplasmic borders.
  • Nuclei are commonly vesicular and exhibited substantial pleomorphism and conspicuous nucleoli.
  • The combination of BRAF mutation and loss of nuclear BAP1 expression thus characterizes a subset of "atypical Spitz tumors" (ASTs) with distinct histologic features.

• in mesothelioma
  • Germline mutation of Bap1 accelerates development of asbestos-induced malignant mesothelioma. (24928783)

 BAP1-mutated tumors (23032617)

• BAP1-mutated clear cell renal cell carcinoma
  • BAP1 is mutated in about 15% of clear-cell renal-cell carcinoma.
  • BAP1 and PBRM1 mutations are largely mutually exclusive.
  • BAP1 and PBRM1 mutation-defined subtypes of clear-cell renal-cell carcinoma with distinct clinical outcomes, a high-risk BAP1-mutant group and a favourable PBRM1-mutant group.

Immunochemistry

 BAP1 immunohistochemistry help to separate benign from malignant mesothelial proliferations. (25634745)

• Combined BAP1 IHC/p16 FISH testing is a highly specific method of diagnosing malignant mesotheliomas when the question is whether a mesothelial proliferation is benign or malignant.
• It is particularly useful when tissue invasion by mesothelial cells cannot be demonstrated.
• However, combined BAP1/p16 FISH testing is not highly sensitive, and negative results do not rule out a mesothelioma.
• The test characteristics of previously proposed markers EMA, p53, GLUT1, IMP3 suggest that, even in combination, these markers are not useful tools in this clinical setting.

References

 BAP1 Immunohistochemistry and p16 FISH to Separate Benign From Malignant Mesothelial Proliferations. Sheffield BS, Hwang HC, Lee AF, Thompson K, Rodriguez S, Tse CH, Gown AM, Churg A. Am J Surg Pathol. 2015 Jan 28. PMID: 25634745

 Germline mutation of Bap1 accelerates development of asbestos-induced malignant mesothelioma. Xu J, Kadariya Y, Cheung M, Pei J, Talarchek J, Sementino E, Tan Y, Menges CW, Cai KQ, Litwin S, Peng H, Karar J, Rauscher FJ, Testa JR. Cancer Res. 2014 Aug 15;74(16):4388-97. doi : 10.1158/0008-5472.CAN-14-1328 PMID: 24928783

 Effects on survival of BAP1 and PBRM1 mutations in sporadic clear-cell renal-cell carcinoma: a retrospective analysis with independent validation. Payal Kapur et al. The Lancet Oncology, Early Online Publication, 16 January 2013. doi : 10 1016/S1470-2045(12)70584-3

 A Distinct Subset of Atypical Spitz Tumors is Characterized by BRAF Mutation and Loss of BAP1 Expression. Wiesner T, Murali R, Fried I, Cerroni L, Busam K, Kutzner H, Bastian BC. Am J Surg Pathol. 2012 Feb 24. PMID: 22367297