Muller, Aixa Elena Soyano

e24161 Background: Pertuzumab-induced gastrointestinal toxicities (PIGT), particularly diarrhea, is the most common adverse event reported in over 70% of patients receiving pertuzumab in combination with chemotherapy. PIGT can result in dose reduction, treatment delay, and discontinuation of chemotherapy. Rifaximin is a minimally absorbed oral antibiotic approved for gastrointestinal tract infections and bacterial overgrowth. Our aim was to evaluate the efficacy of rifaximin in reducing PIGT. Methods: Patients with stage I-III HER2-positive (HER2+) breast cancer who received pertuzumab in combination with docetaxel, carboplatin, and trastuzumab (TCHP) were enrolled. PIGT included diarrhea, abdominal distention, abdominal pain, dyspepsia, stomach pain, and typhlitis. Patients with any PIGT ≥ grade 2 after the first cycle of TCHP received rifaximin 550 mg orally twice daily on days 1-5 in all subsequent cycles of chemotherapy. Patients with PIGT grade < 2 were observed without rifaximin. Simon's Two-Stage design was used. Results: Between 2018-2022, a total of 21 patients were enrolled. One patient was excluded due to significant anemia not meeting the eligibility criteria to proceed with rifaximin after the first cycle of TCHP. Of 20 patients, the median age was 52.5 (39-69) years. 18/20 (90.0%) patients had PIGT ≥ grade 2 after 1 cycle of TCHP with PIGT grade 2 in 15 (83.3%) and grade 3 in 3 (16.7%). PIGT ≥ grade 2 included diarrhea in 14 (70.0%) with grade 2 in 12 (60.0%) and grade 3 in 2 (10.0%), abdominal pain in 9 (45.0%) with grade 2 in 8 (40.0%) and grade 3 in 1 (5.0%), abdominal distension in 3 (15.0%), dyspepsia in 5 (25.0%), and stomach pain in 4 (20.0%) patients. Among 18 patients who received rifaximin, 15 (83.3%; 95% CI 0.586-0.964) had at least 1 cycle with a maximum PIGT grade < 2. This result surpassed the threshold of the Two-Stage analysis. Reduction of individual PIGT symptoms for patients who experienced > grade 2 at baseline after the first cycle of rifaximin was reported in 2/3 (66.7%) for abdominal distention, 8/9 (88.9%) for abdominal pain, 6/14 (42.9%) for diarrhea, 3/4 (75.0%) for stomach pain, and 4/5 (80.0%) for dyspepsia. No patients experienced > grade 2 typhilitis at baseline and during treatment. Treatment is well tolerated, with no significant grade 3+ adverse event related to rifaximin observed. Among patients who received rifaximin, there was no treatment delay or discontinuation of pertuzumab related to PIGT. Conclusions: PIGT is a debilitating side effect observed in most patients receiving pertuzumab. A short course of rifaximin after each cycle of treatment is a well-tolerated treatment option that significantly reduces PIGT in patients receiving pertuzumab in combination with chemotherapy. Clinical trial information: NCT04249622 .

2027 Background: Breast cancer related leptomeningeal disease (BC-LMD) is a dire diagnosis for 5-8% of breast cancer patients with overall survival (OS) measured in weeks without treatment. As new treatments prolong survival with breast cancer, the risk of developing BC-LMD may be increasing. We hypothesized that the rate of BC-LMD diagnosis increased significantly with time. We also predicted that OS with BC-LMD had changed with time and in relationship to molecular subtype and treatment following BC-LMD diagnosis. Methods: With approval of the local Scientific Research Committee and IRB, we conducted a retrospective analysis of medical records for patients treated or diagnosed with breast cancer at MCC from 2011-2020. Patient demographics, tumor characteristics, treatments, and outcomes were collected. Kaplan Meier survival curves were used to determine median overall survival (OS), progression of disease, and differences by molecular subtype. Univariate and multivariate analyses were used to determine characteristics of primary tumors and treatments which affected OS. Results: Of the 133 cases identified, significantly more were diagnosed between 2016-2020 than 2011-2015 (p < 0.01). Significant increases were seen in HER2+ and TNBC patients (p < 0.05) but not for ER/PR positive (HR+) disease (p = 0.058). HER2+ LMD associated with longest overall survival (OS; 7mths) followed by HR+ disease (3mths) and TNBC with the shortest OS (2mths). Systemic metastases preceded BC-LMD diagnosis in 72% of cases and CNS metastases in 85% of cases. HER2+ disease also conferred increased survival after CNS metastases were diagnosed until progression to LMD (8mth vs 2mth for HR+ and 1mth for TNBC LMD; p < 0.05). Positive impact on survival by HER2 targeted therapies may account for improved OS in this population. Other factors which increased OS generally were: WBRT, continuation of systemic therapy, delivery of intrathecal chemotherapy, and participation in clinical trials. Having TNBC and decision to defer treatment were associated with reduced OS. Conclusions: This study highlights the importance of identifying patients with BC-LMD early and with the intention to treat. Prospective clinical trials and population-based studies are needed to advance treatment of BC-LMD.