Loss of BAP1 expression is very rare in breast carcinoma

Targeting BAP1 with small compound inhibitor for colon cancer treatment

BRCA1-associated protein-1 (BAP1) is a ubiquitin C-terminal hydrolase domain-containing deubiquitinase. The gene encoding BAP1 is mutated in various human cancers, including mesothelioma, uveal melanoma and renal cell carcinoma. BAP1 plays roles in many cancer-related cellular functions, including cell proliferation, cell death, and nuclear processes crucial for genome stability, such as DNA repair and replication. While these findings suggest that BAP1 functions as a tumor suppressor, recent data also suggest that BAP1 might play tumor-promoting roles in certain cancers, such as breast cancer and hematopoietic malignancies. Here, we show that BAP1 is upregulated in colon cancer cells and tissues and that BAP1 depletion reduces colon cancer cell proliferation and tumor growth. BAP1 contributes to colon cancer cell proliferation by accelerating DNA replication and suppressing replication stress and concomitant apoptosis. A recently identified BAP1 inhibitor, TG2-179-1, which seems to covalently bind to the active site of BAP1, exhibits potent cytotoxic activity against colon cancer cells, with half-maximal inhibitory concentrations of less than 10 μM, and inhibits colon tumor growth. TG2-179-1 exerts cytotoxic activity by targeting BAP1, leading to defective replication and increased apoptosis. This work therefore shows that BAP1 acts oncogenically in colon cancer and is a potential therapeutic target for this cancer. Our work also suggests that TG2-179-1 can be developed as a potential therapeutic agent for colon cancer.

BAP1-defficient breast cancer in a patient with BAP1 cancer syndrome

BAP1 cancer syndrome is a rare and highly penetrant hereditary cancer predisposition. Uveal melanoma, mesothelioma, renal cell carcinoma (RCC) and cutaneous melanoma are considered BAP1 cancer syndrome core cancers, whereas association with breast cancer has previously been suggested but not confirmed so far. In view of BAP1 immunomodulatory functions, BAP1 alterations could prove useful as possible biomarkers of response to immunotherapy in patients with BAP1-associated cancers. We present a case of a patient with BAP1 cancer syndrome who developed a metastatic breast cancer with loss of BAP1 demonstrated on immunohistochemistry. She carried a germline BAP1 likely pathogenic variant (c.898_899delAG p.(Arg300Glyfs*6)). In addition, tumor tissue sequencing identified a concurrent somatic variant in BAP1 (partial deletion of exon 12) and a low tumor mutational burden. As her triple negative tumor was shown to be PD-L1 positive, the patient was treated with combination of atezolizumab and nab-paclitaxel. She had a complete and sustained response to immunotherapy even after discontinuation of nab-paclitaxel. This case strengthens the evidence for including breast cancer in the BAP1 cancer syndrome tumor spectrum with implications for future cancer prevention programs. It also indicates immune checkpoint inhibitors might prove to be an effective treatment for BAP1-deficient breast cancer.

Immunohistochemical Evaluation of BAP1 Expression in Breast Cancer with Known BRCA1 and BRCA2 Mutations and Comparison with Histopathological Features

Introduction. BRCA-mutated breast cancers have specific pathological characteristics. BAP1 is a tumor suppressor gene that is important in many cancers with different pathways. The relationship between BRCA1 mutation and BAP1 immunohistochemical staining is still unclear. Our aim is to determine whether BAP1 immunohistochemical expression indicates BRCA mutation status in breast carcinomas with specific pathological characteristics. In addition, we aim to determine the histopathological characteristics of tumors according to BRCA mutations. Methods. Histomorphology, molecular subtypes and BAP1 immunohistochemical expression patterns of the BRCA1/BRCA2 mutated and non-mutated tumors were evaluated. The BAP1 immunohistochemical stain was applied to nine tumor tissues with the BRCA1 mutation, six tumor tissues with the BRCA2 mutation, and 16 tumor tissues without any BRCA mutation. Pearson's chi square test and the Fisher Freeman Halton test were used to analyze the associations between the datas. The statistical significance was considered as P value of <.05. Results. Immunohistochemical BAP1 loss was not detected in any mutated or non-mutated tumor group. BRCA1 mutated tumors had the statistically highest histopathological grade (P = .04) and BRCA1/2 mutated tumors had significant immunohistochemical triple negative expression pattern (P = .01). Conclusions. Intrinsic and histopathological characteristics may vary between BRCA1 mutated and non-BRCA1 mutated tumors. Also, BAP1 loss was not detected in BRCA mutated breast tumors because of several effects of BAP1 that are non-related with BRCA in the cell cycle.

Diagnostic Utility of BAP1, EZH2 and Survivin in Differentiating Pleural Epithelioid Mesothelioma and Reactive Mesothelial Hyperplasia: Immunohistochemical Study

Background: Epithelioid mesothelioma (EM) is the commonest subtype of malignant pleural mesothelioma. Its histopathological discrimination from reactive mesothelial hyperplasia (RMH) could be challenging. Thus, an immunohistochemical panel is mandatory for better discrimination. BAP1 is a newly identified diagnostic marker whose loss is specific to malignant mesothelioma. EZH2 overexpression is reported in different cancers, but its relation to BAP1 in malignant mesothelioma has not been fully understood. Survivin expression is said to be significantly higher in EM than in non-neoplastic pleural tissue, but its diagnostic utility as an immunohistochemical marker has not been thoroughly investigated in this field. To the best of our knowledge, no previous studies have been conducted to assess the diagnostic accuracy of the combined use of these three nuclear markers (BAP1, EZH2 and Survivin) in discriminating pleural EM from RMH. Methods: This retrospective study includes two groups: 81 cases of pleural EM and 67 cases of RMH, retrieved from the archives of Pathology Department of Ain Shams University Hospitals and Ain-Shams University Specialized Hospital during the period from January 2016 to December 2019. An immunohistochemical study was performed using BAP1, EZH2 and Survivin antibodies. Results: There were highly statistically significant relations between study groups as regards the studied markers (p = 0.001 for each). The specificity was 100% for all combinations of immunohistochemical markers. Sensitivity of any combination of the immunohistochemical markers used in this study was found to be higher than the sensitivity of any of these markers used individually. The combination of all three markers showed the highest diagnostic accuracy (95.9%) and the highest sensitivity (92.6%). However, the combination of Survivin and EZH2 yielded the same diagnostic accuracy and sensitivity. Conclusion: Adding EZH2, Survivin and BAP1 to the diagnostic IHC panel for differentiating pleural EM and RMH could enhance diagnostic sensitivity. Moreover, Survivin is a potentially promising marker in this context, especially when combined with EZH2.

The Melanoma and Breast Cancer Association: An Overview of their 'Second Primary Cancers' and the Epidemiological, Genetic and Biological correlations

This study reviews the relevant epidemiological studies associating cutaneous melanoma and breast carcinomas and provides an overview of the possible genetic, biological and bias factors that underpin this relationship. Standardised incidence ratio (SIR) for primary cutaneous melanoma after breast carcinoma ranged from 1.16 to 5.13 and ranged from 1.03 to 4.10 for primary breast carcinoma after cutaneous melanoma. Epidemiological studies highlight age, gender and use of radiotherapy and chemotherapy as potential risk factors for second primary cancers (SPCs). Mutations in BRCA2, CDKN2A, CDK4 and BAP1 may partly underlie any SPC association. The impact of socio-cultural factors and surveillance bias may be attributed to the findings of SPC partially or entirely. In conclusion, this study has highlighted the association between breast carcinoma and melanoma and identified various factors for further research and the optimised management of patients with both cancers.

BAP1 expression is prognostic in breast and uveal melanoma but not colon cancer and is highly positively correlated with RBM15B and USP19

BAP1 is a tumor suppressor gene important to the development and prognosis of many cancers, especially uveal melanoma (UM). Its role in more common cancers such as breast and colon cancer is largely unknown. We collected the transcriptome profiling data sets from the TCGA uveal melanoma (TCGA-UVM), breast cancer (TCGA-BRCA), and colon cancer (TCGA-COAD) projects to analyze the expression of BAP1. We found that patients with UM and breast cancer, but not colon cancer, who died had a lower level of BAP1 gene expression compared to surviving patients. Importantly, in breast cancer patients, the lowest BAP1 expression levels corresponded to the dead young patients (age at diagnosis < 46). Since the number of cases in TCGA-BRCA was much higher than TCGA-UVM, we obtained highly correlated genes with BAP1 in invasive breast carcinomas. Then, we tested if these genes are also highly correlated with BAP1 in UM and colon cancer. We found that BAP1 is highly positively correlated with RBM15B and USP19 expression in invasive breast carcinoma, UM, and colon adenocarcinoma. All three genes are located in close proximity on the 3p21 tumor suppressor region that is commonly altered in many cancers.