PBRM1 genomic alterations as a predictive biomarker to immune checkpoint inhibitors (ICI) and/or anti-angiogenic therapies (anti-VEGF) in metastatic renal cell carcinoma (mRCC): A systematic review and meta-analysis

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Background: Combination therapy with ICI and anti-VEGF has become the standard first-line (1L) therapy for metastatic clear cell RCC (mccRCC). However, about 25% of patients (pts) are long responders to anti-VEGF monotherapy. PBRM1 genomic alterations (ga) are present in around 40% mccRCC pts and contradictory results have been reported about its role as a predictive biomarker. We performed a systemic review and meta-analysis to assess the role of PBRM1 ga as a predictive biomarker of response to ICI, anti-VEGF, or its combination. Methods: A systematic review of PubMed, EMBASE, Cochrane, and Web of Science databases was performed (February 2022) to identify studies involving mRCC pts who received systemic therapy and had PBRM1 status and clinical outcomes reported. Study design, baseline characteristics, treatment data, and hazard ratios (HRs) with 95% confidence intervals (CI) for each clinical outcome were extracted. HRs were combined across studies using a random effect model. The primary endpoint was to correlate PBRM1 status with progression-free survival (PFS) to anti-VEGF, ICI, or its combination. Results: The systematic review included 12 out of 892 publications (n = 6528 pts), 98% (n = 6372) mccRCC; 3297 pts (51%) treated with anti-VEGF monotherapy, 1574 (24%) ICI (PD-L1 (n = 1019, 65%) or CTLA4 + anti PD-L1 (n = 555, 35%)), 997 pts (15%) anti-VEGF + ICI, and 660 pts (10%) with other therapies (e.g., mTORi or INF). PBRM1 status was assessed by NGS in 3841 pts (59%) and detected in 1595 (41%). Nine out of 12 publications were considered for the meta-analysis; excluding those with duplicated pts or lack of information. Six studies (n = 2593 pts) evaluated PBRM1 status in first-line (1L) therapies, including anti-VEGF in monotherapy (n = 1487, 57%) and ICI (n = 1106, 43%; combined w/anti-VEGF (n = 773), w/CTL4 (n = 262) or in monotherapy (n = 71)). In 1L setting, PBRM1 ga pts had longer PFS under monotherapy with anti-VEGF ( PBRM1 ga 44%; HR = 0.74 (95% CI, 0.62 - 0.88), p < 0.01) but not under ICI ( PBRM1 ga = 42%; HR = 1 (95% CI, 0.85 - 1.17), p = 0.38) nor ICI + anti-VEGF treatment ( PBRM1 ga = 33.5%; HR = 0.93 (95% CI, 0.73 - 1.18), p = 0.56). Two studies evaluated PBRM1 status in second line (2L) ICI-treated mRCC pts (n = 517 pts). PBRM1 ga pts had longer PFS under ICI in 2L ( PBRM1 ga = 36%, HR = 0.64 (95% CI, 0.49 - 0.83), p = 0.0007). Conclusions: mRCC pts with PBRM1 ga showed longer PFS to 1L anti-VEGF and 2L ICI therapy, supporting its role as a predictive biomarker. Anti-VEGF + ICI combination de-escalation strategies merits further investigation in PBRM1 ga mRCC patients.

Case Report: A Case Study Documenting the Activity of Atezolizumab in a PD-L1-Negative Triple-Negative Breast Cancer

The immune checkpoint inhibitor atezolizumab is approved for PD-L1-positive triple-negative breast cancer (TNBC). However, no activity of atezolizumab in PD-L1-negative TNBC has been reported to date. Here, we present the case study of a woman with TNBC with low tumor infiltrating lymphocytes and PD-L1-negative disease, which achieved a significant response to atezolizumab monotherapy and durable response after the combination of atezolizumab and nab-paclitaxel. The comprehensive genomic analysis that we performed in her tumor and plasma samples revealed high tumor mutational burden (TMB), presence of the APOBEC genetic signatures, high expression of the tumor inflammation signature, and a HER2-enriched subtype by the PAM50 assay. Some of these biomarkers have been shown to independently predict response to immunotherapy in other tumors and may explain the durable response in our patient. Our work warrants further translational studies to identify biomarkers of response to immune checkpoint inhibitors in TNBC beyond PD-L1 expression and to better select patients that will benefit from immunotherapy.