BAP1

BAP1 (BRCA1‑associated protein‑1) is a tumour‑suppressor deubiquitinase located on chromosome 3p21.1, and loss of its nuclear expression on IHC is clinically significant in several malignancies. Loss of BAP1 helps differentiate malignant from benign mesothelial proliferations and is also useful in distinguishing metastatic uveal melanoma, typically BAP1‑negative in at least 77% of cases from metastatic cutaneous melanoma, which is usually BAP1‑retained (only ~5% negative). Pathologists use BAP1 IHC staining primarily for prognostication in uveal melanoma and for diagnostic differentiation in mesothelioma and melanocytic lesions (1).

Recommended Controls

The criteria for acceptable is nuclear. The mesothelioma shows loss of nuclear staining. Normal lung shows positive staining in the normal mesothelium and lung epithelium. Lung adenocarcinoma should show positive staining. The recommended control for BAP1 would be a tumour (mesothelioma or melanoma) which should show a loss of staining and a lung adenocarcinoma with normal lung, which will be the positive control.

Expected staining pattern

Lung adenocarcinoma

Mesothelioma

Normal lung

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.