143P A single institution’s real-world experience with the neoadjuvant Keynote-522 treatment regimen

Pembrolizumab is now part of a neoadjuvant (NA) regimen for patients (pts) with triple-negative breast cancer (TNBC) that results in a higher pathologic complete response (pCR) rate compared to chemotherapy alone (Keynote 522). However, real-world experience will reveal the true tolerability of the regimen. This retrospective review at a single tertiary care center aims to evaluate side effects (SEs), treatment changes/interruptions, urgent care (UC), ER visits, and hospitalizations in pts who received NA Keynote 522 (pembro) compared to chemotherapy alone (chemo), and to compare to the results of the phase III Keynote 522 trial. 229 patient charts were reviewed. Included pts had stage II/III TNBC and received NA pembro from 2/2020 - 8/2022 or NA chemo from 7/2017 - 1/2020. Demographics, blood test results, # of UC, ER visits, and hospitalizations during treatment were collected. Provider notes and plans were reviewed for SEs and changes or interruptions during treatment. Data were analyzed using SPSS Statistics. Chi-square tests were performed on categorical variables. There were 28 and 45 patients in the pembro and chemo groups, respectively. Age, race, ethnicity, & surgery type were similar between groups. Pts in the pembro group had more advanced stage at diagnosis (p = 0.003). pCR rate was higher in the pembro group (53.6% vs 35.6%). Neutropenia, rash, infusion reaction, thyroid abnormalities, and grade 3 LFT elevations were more common in the pembro group (p = <0.001, <0.001, 0.01, <0.001 and 0.025). Pts in the pembro group had more treatment interruptions (67.9% vs 13.3%, p < 0.001), changes due to SEs (57.1% vs 11.1%, p < 0.001), and ER and UC visits (p = 0.012 and p <0.001). More frequent SEs were observed in the pembro group compared to the Keynote 522 trial pembro arm (anemia (96.4% vs 55.1%), neutropenia (71.4% vs 46.7%), fatigue (89.3% vs. 41.1%), & neuropathy (57.1% vs 19.7%)). In this study, the Keynote 522 regimen was more poorly tolerated compared to chemo alone with increased SEs and treatment changes/interruptions. While the pCR rate was higher, potential SEs and treatment changes/interruptions must be considered when selecting appropriate pts for treatment.