Abstract RF02-04: A phase III study comparing trastuzumab emtansine with trastuzumab, pertuzumab, and docetaxel in older patients with metastatic HER2-positive breast cancer. (JCOG1607 HERB TEA study)

Abstract Background A combination of trastuzumab, pertuzumab, and docetaxel (HPD) is recommended as first-line treatment for patients with HER2-positive metastatic breast cancer. For older patients, it is difficult to maintain a relative dose intensity, which often impairs their quality of life. A new standard treatment option for older patients is required with less toxicity and non-inferior efficacy compared to HPD. Methods The eligibility criteria were as follows: age 65 years and older, HER2-positive metastatic breast cancer, no previous systemic treatment with chemotherapy and anti-HER2 targeted drugs, ECOG PS 0–2 for 65–74 years or 0–1 for 75 years or older, and adequate organ function. Treatment consisted of trastuzumab emtansine (T-DM1) 3.6 mg/kg every 3 weeks or HPD (trastuzumab 8 mg/kg, then 6 mg/kg, pertuzumab 840 mg, then 420 mg/body, and docetaxel 60 mg/m2, could be escalated to 75 mg/m2 if there were no unmanageable toxicity) every 3 weeks after a 1:1 ratio randomization. The trial was designed to achieve 70% power to confirm the non-inferiority of T-DM1 to HPD at a one-sided alpha of 5% with a non-inferiority margin of 1.35 in terms of the hazard ratio (HR) for overall survival (OS) as the primary endpoint. With a median OS of 30 months in both arms, 6.5 years of accrual, and 5 years of follow-up, the planned sample size was 250. Secondary endpoints were progression-free survival (PFS), response rate (RR), adverse events, cumulative breast cancer-specific mortality (BCSM), safety, and deterioration of activities of daily living. (Clinical Trial Information: UMIN000030783). Results In total, 148 patients were enrolled between January 2018 and March 2023. A total of 135 patients were assessed in the preplanned first interim analysis. The median patient age was 72 years (range 65-88) in the T-DM1 arm and 71 (65-84) in the HPD arm. The proportion of estrogen receptor-positive (10%) patients was well balanced between both arms (49.3 and 55.6%, respectively). Of these patients, 64.8% had stage IV disease and 35.2% had recurrent disease. T-DM1 was not non-inferior to HPD (HR 1.487; 99.9% CI, 0.288 to 7.678) in terms of OS. The median PFS was 9.8 months in the T-DM1 arm and 18.4 months in the HPD arm (HR 1.749; 95%CI, 1.124-2.723). Response rates were lower in the T-DM1 arm than that of the HPD arm (52.7% 95% CI, 38.8-66.4 and 76.8% 95% CI, 63.6-87.0, respectively) (p=0.099). BCSM was higher in the T-DM1 arm than that of the HPD arm (HR 1.617; 95% CI, 0.764-3.425). Grade 3 and higher neutropenia were less common in the T-DM1 arm than in the HPD arm (0 vs. 30.4%); however, thrombocytopenia was more common in the T-DM1 arm than in the HPD arm (16.9 vs. 0%). Grade 3 or more non-hematological adverse events were less common and lower in the T-DM1 arm (35.2%) than in the HPD arm (58.6%), including fatigue (5.6% vs. 22.9%), diarrhea (0% vs. 11.4%), appetite loss (8.5% vs. 11.4%), and febrile neutropenia (0% vs. 10.0%), which reduced the quality of life in older patients with HER2-positive metastatic breast cancer. Conclusion T-DM1 was not non-inferior to HPD in terms of OS. However, T-DM1 showed better tolerability in terms of frequency and severity of adverse events. HPD will continue to be the standard of care as the first-line treatment for older patients with HER2-positive metastatic breast cancer. Older patients with breast cancer have heterogeneous health conditions. A subset analysis according to age or geriatric assessment may identify the subpopulation of older patients with HER2-positive metastatic breast cancer for whom T-DM1 is an optional treatment. Citation Format: Akihiko Shimomura, Kenji Tamura, Keita Sasaki, Ryo Sadate, Akihiko Suto, Masataka Sawaki, Naohito Yamamoto, Tomoyuki Yoshiyama, Takako Hayashi, Eriko Tokunaga, Takashi Yamanaka, Chikako Shimizu, Tadahiko Shien, Hiroji Iwata. A phase III study comparing trastuzumab emtansine with trastuzumab, pertuzumab, and docetaxel in older patients with metastatic HER2-positive breast cancer. (JCOG1607 HERB TEA study) abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr RF02-04.