Olema Pharmaceuticals Reports Initial Clinical Data From The Phase 1 Study of OP-3136, A KAT6 Inhibitor, At 2026 ASCO Annual Meeting; OP-3136 Monotherapy Was Well-tolerated With No Dose-limiting Toxicities Observed And No Discontinuations Due To Treatment-related Adverse Events; OP-3136 Shows Evidence Of Anti-tumor Activity Across Multiple Solid Tumor Types

Olema Pharmaceuticals, Inc. (("Olema" or "Olema Oncology", NASDAQ:OLMA), a clinical-stage biopharmaceutical company focused on the discovery, development, and commercialization of targeted therapies for breast cancer and beyond, today announced preliminary clinical data from the Phase 1 study of OP-3136, a potent lysine acetyltransferase 6 (KAT6) inhibitor. The data will be presented in a poster presentation on May 30, 2026 at the American Society of Clinical Oncology (ASCO) Annual Meeting taking place in Chicago, Illinois. Olema will also present a trial-in-progress poster for the Phase 3 OPERA-02 trial of palazestrant in combination with ribociclib in frontline estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) metastatic breast cancer.

"We are pleased to share the initial Phase 1 data for OP-3136, which demonstrated acceptable tolerability and promising anti-tumor activity as a monotherapy across multiple dose levels in various advanced solid tumor types," said Sean P. Bohen, M.D., Ph.D., President and Chief Executive Officer of Olema Oncology. "The decreases in tumor size observed in over two-thirds of evaluable patients and evidence of on-target engagement reinforce our confidence in OP-3136 as a potential best-in-class KAT6 inhibitor and a potentially differentiated option for difficult-to-treat cancers. We look forward to progressing OP-3136 in development, particularly in combination with palazestrant in metastatic breast cancer."

The Phase 1 study evaluates dose escalation followed by dose expansion of OP-3136 in patients with ER+/HER2- advanced breast cancer (ABC), metastatic castration-resistant prostate cancer (mCRPC), and metastatic non-small cell lung cancer (mNSCLC). In Part 1A, OP-3136 monotherapy was administered orally once daily in 28-day cycles across dose levels from 2 mg to 45 mg. As of the March 2, 2026 data cut-off, 32 heavily pretreated patients who became resistant or intolerant to standard of care treatments were enrolled in this cohort.

Key Findings

Safety and Tolerability

• OP-3136 monotherapy was well-tolerated with no dose-limiting toxicities observed across the evaluated daily dose range up to 45 mg per day orally.
• Most treatment-related adverse events (TRAEs) were grade 1 or 2; no grade 4 or 5 TRAEs were observed. TRAEs were manageable with dose modifications; no treatment discontinuations occurred due to TRAEs.
• The most common TRAEs were dysgeusia (81% any grade; 56% grade 1, 25% grade 2), anemia (38% any grade; 6% grade 3), and neutropenia (34% any grade; 28% grade 3).
  
  
  
   

Efficacy and Target Engagement

• Among 19 response-evaluable patients across dose levels and tumor types, tumor shrinkage was observed in 13 patients; partial responses (PR) were observed in 3 patients with measurable disease, with 2 confirmed PRs and 1 unconfirmed PR.
• The longest duration of treatment is 62 weeks.
• 11 patients remain on treatment, including 9 with ABC and 2 with mCRPC.
• Across all doses tested, OP-3136 demonstrated rapid, sustained, and significant reduction in levels of lysine 23 of histone H3, a direct target of KAT6, consistent with on-target KAT6 inhibition.