Patients with ovarian clear cell carcinoma (OCCC) whose tumors harbor specific mutations in the PPP2R1A gene demonstrated dramatically improved survival following immunotherapy treatment, according to new research from The University of Texas MD Anderson Cancer Center published in Nature.
The study analyzed outcomes in 34 patients with platinum-resistant OCCC treated with combination immune checkpoint inhibitors durvalumab (anti-PD-L1) and tremelimumab (anti-CTLA-4). Patients with PPP2R1A mutations achieved a median overall survival of 66.9 months compared to just 9.2 months for those without these mutations (hazard ratio 0.40; 95% CI 0.15-1.08; one-sided log-rank P = 0.031).
Clinical Trial Results Reveal Biomarker Significance
The research focused on patients enrolled in a Phase II clinical trial (NCT03026062) investigating combination immunotherapy in platinum-resistant ovarian cancer. Among the 34 patients analyzed, 11 (32.4%) harbored somatic mutations in PPP2R1A, which encodes the predominant scaffold subunit of the PP2A phosphatase complex.
Most PPP2R1A mutations (81.8%) occurred at the hotspot codon Arg183, with five patients carrying the R183W mutation and four carrying the R183Q mutation. The remaining patients had S256F and W257G missense mutations. All observed mutations are known to impair binding of the scaffold A subunit to regulatory B subunits of PP2A, conferring loss of function.
The median follow-up was 13.7 months, with overall median survival of 14.3 months (95% CI 5.8-22.9 months) across the entire cohort. The 6-month and 1-year survival probabilities were 0.68 (95% CI 0.54-0.85) and 0.56 (95% CI 0.41-0.75), respectively.
Exceptional Responders Drive Discovery
Three exceptional responder patients provided initial evidence for the PPP2R1A association. The first patient, harboring a PPP2R1A R183Q mutation, received ipilimumab and nivolumab for 15 months and survived 5.5 years after starting immunotherapy. Two additional exceptional responders with PPP2R1A (R183W) and AKT3 (R249H) mutations remained alive 5.8 and 5.1 years after treatment initiation, respectively.
"Developing effective immunotherapies for ovarian cancer, including rare subtypes like ovarian clear cell carcinoma, remains a significant unmet clinical need," said co-senior author Amir Jazaeri, M.D., professor of Gynecologic Oncology and Reproductive Medicine. "Our study is the first to demonstrate the clinical importance of PPP2R1A mutations, and it opens the door to new strategies that could benefit many more patients."
Delayed Response Pattern Observed
Analysis of clinical courses revealed that the survival benefit associated with PPP2R1A mutations was characterized by delayed responses that sometimes followed initial progression or stable disease. All patients were enrolled on clinical trials allowing continuation of immunotherapy beyond apparent progression, which may have contributed to durable disease control in PPP2R1A-mutated tumors.
Higher rates of grade 3 or higher immune-related adverse events were noted in PPP2R1A mutation carriers (45.5% versus 13.0% for non-carriers; P = 0.079), consistent with previous studies demonstrating positive correlation between immune-related adverse events and favorable outcomes with immune checkpoint blockade.
Laboratory Studies Confirm Causal Relationship
Parallel laboratory research demonstrated that targeting PPP2R1A both in vitro and in vivo enhanced immunotherapy responses, suggesting a causal link rather than merely correlative association. The studies utilized genetically modified cell lines and humanized patient-derived xenograft models to validate the mechanistic basis for improved immunotherapy sensitivity.
Validation Across Multiple Cancer Types
To confirm broader applicability, researchers analyzed two additional independent cohorts: patients with endometrial cancer and over 9,000 patients with multiple cancer types who received immunotherapy. These analyses confirmed improved overall survival following immunotherapy in patients with tumor PPP2R1A mutations across different cancer types.
The validation in endometrial cancer is particularly relevant, as PPP2R1A mutations occur in relatively higher prevalence in high-risk histologies including serous, clear cell, carcinosarcoma, and mesonephric-like adenocarcinoma subtypes.
Therapeutic Implications and Future Directions
The findings suggest PPP2R1A mutations could serve as a valuable predictive biomarker for immunotherapy response across multiple cancer types. Since PPP2R1A mutations are relatively uncommon, the research team is investigating whether targeting the PP2A pathway pharmacologically could extend similar benefits to a broader patient population.
"Not only did we identify a new biomarker in ovarian cancer, but we also confirmed survival benefits in other cancer types," Jazaeri noted. "Since PPP2R1A mutations are relatively uncommon, we believe the same benefits may be possible by targeting the PPP2A pathway using drugs, and we currently are evaluating this in a clinical trial at MD Anderson."
The study represents a collaborative effort led by co-senior authors Jazaeri; Linghua Wang, M.D., Ph.D., associate professor of Genomic Medicine; and Rugang Zhang, Ph.D., chair of Experimental Therapeutics, with co-lead first authors Yibo Dai, Minghao Dang, Ph.D., Anne Knisely, M.D., and Mitsutake Yano, M.D., Ph.D.
