Abstract CT012: PARTNER Trial: Neoadjuvant olaparib in triple negative breast cancer (TNBC)

Abstract Background: TNBCs in patients (pts) who are germline BRCA wild type (gBRCAwt) may show homologous recombination deficiency and genomic instability, resulting in a BRCA-like phenotype. The PARTNER Trial tested olaparib in combination with neoadjuvant carboplatin and paclitaxel in pts with TNBC (gBRCAwt). Methods: Pts with TNBC diagnosed locally were confirmed centrally with immunohistochemistry for ER, PR, HER2 and EGFR, CK5/6 and AR to define basal-like TNBC, before entry to the PARTNER trial. Pts were gBRCAwt. Tumours were assessed for tumour infiltrating lymphocytes (TILs). Pts were randomised 1: 1 to research (R) and control arms (C). Pts received neoadjuvant carboplatin AUC 5, day (d) 1, with paclitaxel 80mg/m2 d1, 8, 15, every (q) 3 weeks (w), x 4 cycles (cy), +/- olaparib 150mg bd, po, d3-14 q 3w. Then all pts had 3cy of anthracycline chemotherapy before surgery. Primary endpoint was pathological complete response (pCR), and secondary endpoints included event-free survival (EFS), and overall survival (OS). A total of 454 patients were needed to attest 90% power with 5% significance assuming pCR rate of 50% in C and 65% in R. Results: From Sept 2016 to Dec 2021, 559 pts with TNBC (gBRCAwt) were randomised at 29 UK centres. Data cut-off was 30/11/23 with median (med) follow-up of 38 months (m). There were 276 R and 264 C pts in the intention-to-treat population. Pt and tumour characteristics were balanced between the arms: med pt age 49 years; 95% ECOG 0; 36% previous oophorectomy or post-menopausal; 95% tumour size ≤50mm; TILS score ≥60% in 22%. In R, 88% received at least 80% of the planned olaparib dose. More than 90% of patients in both R and C received at least 80% of the planned carboplatin (R 96% and C 94%) and paclitaxel (R 100% and C 99%) doses. Of 543 pts, 141 (51. 1%) in R and 140 (52. 4%) in C had a pCR with a difference of -1. 3% (95% CI -9. 7% to 7. 0%, p-value=0. 753). Percentage of pts with pCR increased with increasing TILs; pCR rate was 32% with TILs 0-10%, increasing to 67% with TILs 90-100%. Estimated EFS at 36 months (m) was 80% in R and 79% in C (log-rank p0. 9) ; estimated OS at 36m was 90% in R and 87. 2% in C (log-rank p=0. 8). Estimated 36m EFS rate was 90. 4% (95% CI, 86. 4 to 94. 5) in pts with pCR and 70% (95% CI, 64. 2 to 76. 2) in pts with non-pCR (HR=0. 3, 95% CI 0. 2 to 0. 4; p 0. 001). Estimated 36m OS was 95. 7% (95% CI, 93. 0 to 98. 5) in pts with pCR, and 83% (95% CI, 78 to 88. 2) in pts with non-pCR (HR=0. 2, 95% CI 0. 1 to 0. 3; p 0. 001). More events and deaths were observed in non-pCR pts compared to pCR pts regardless of the treatment received. Conclusions: Neo-adjuvant olaparib in the dose and schedule tested, in addition to carboplatin/taxol and anthracycline chemotherapy in basal-like TNBC in gBRCAwt patients, did not improve pCR rates, EFS or OS. Pts who achieved a pCR had significantly better EFS and OS than those with non-pCR. These results are in marked contrast to the significant benefit of olaparib in those with gBRCA mutations reported in parallel. Citation Format: Jean E. Abraham, Karen Pinilla, Louise Grybowicz, Alimu Dayimu, Nikolaos Demiris, Caron Harvey, Lynsey M. Drewett, Rebecca Lucey, Alexander Fulton, Anne N. Roberts, Joanna R. Worley, Anita Chhabra, Wendi Qian, Richard M. Hardy, Stephen Chan, Tamas Hickish, Devashish Tripathi, Ramachandran Venkitaraman, Mojca Persic, Shahzeena Aslam, Daniel Glassman, Sanjay Raj, Annabel Borley, Jeremy P. Braybrooke, Stephanie Sutherland, Emma Staples, Lucy C. Scott, Mark Davies, Cheryl A. Palmer, Margaret Moody, Mark J. Churn, Jacqueline C. Newby, Mukesh B. Mukesh, Amitabha Chakrabarti, Rebecca R. Roylance, Philip C. Schouten, Nicola Levitt, Karen McAdam, Anne C. Armstrong, Ellen R. Copson, Emma McMurtry, Marc Tischkowitz, Elena Provenzano, Helena Earl, PARTNER Trial Group. PARTNER Trial: Neoadjuvant olaparib in triple negative breast cancer (TNBC) abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT012.