Abstract P3-14-02: A cohort study to evaluate the efficacy and safety of postoperative adjuvant therapy in HER2-positive elderly breast cancer patients (RESPECT-cohort study)

Background: The randomized controlled trial (RCT) is accepted as the standard clinical trial to decide a standard therapy, but it remains unclear whether or not elderly patients benefit as much as other patients from participation in an RCT. In the RESPECT study (NCT01104935), the relative value of trastuzumab (H) monotherapy as an adjuvant treatment was compared in an RCT with the standard combination treatment with chemotherapy (H+CT) in patients over 70 years old with HER2-positive invasive breast cancer (BC) who received curative surgery. This cohort study was aimed at comparing prognoses between RCT participants (RCT group) and non-participants (Cohort group). Methods: Patients were divided into RCT participants, and those who did not agree to participate in the RCT despite meeting the eligibility criteria and receiving the explanation given by the investigator. In the RCT group patients were randomized to H or H+CT; in the Cohort group treatment was selected for each patient based on the discretion of the treating physician and the patient9s wishes without intervention. Treatment categories were divided into three groups: (1) trastuzumab monotherapy group (cH group), (2) trastuzumab plus chemotherapy group (cH+CT group), and (3) those who received either no therapy at all, or any other anticancer therapies without H (cOther group). The primary endpoint was disease-free survival (DFS). Secondary endpoints were overall survival (OS), relapse-free survival, safety, health-related quality of life (HRQOL) and comprehensive geriatric assessment. Results: A total of 275 patients in the RCT group and 123 patients in the Cohort group, in total 398 patients, were enrolled in this study between October 2009 and October 2014. The median age was 74.0 years in the RCT group, 74.5 years in the Cohort group and the median follow-up time was 4.1 years and 3.2 years, respectively. Patients were classified as Stage I: 41.8%, 42.5%; IIA: 41.5 %, 40.8%; IIB: 13.5%, 13.3%; and IIIA: 1.5%. 3.3%, respectively (P = 0.51), there were no significant differences between the two groups. Treatment categories in the Cohort group were: (1) cH group; 43% (n = 52), (2) cH+CT group; 30% (n = 36), cOther group; 27% (n = 32). The planned analysis showed that DFS at 3 years was 91.4% in the RCT group vs 89.3% in the Cohort group (adjusted hazard ratio (HR) = 1.30; 95%CI, 0.72-2.35, P = 0.38). In patients in the cH+CT, cH and cOther group, DFS at 3 years was 92.3%, 89.2% and 82.5%, respectively. DFS in patients in the cH+CT and the cH group was significantly better than that of the cOther group (adjusted HR = 3.79; 95%CI = 1.35-10.64, P = 0.01). DFS in the cH group showed a better tendency compared with cOther (adjusted HR = 2.59; 95%CI, 0.87-7.73, P = 0.08). The incidence of grade 3/4 non-hematological adverse events in the RCT group was relatively higher compared with the Cohort group (18.5% vs 10.8 %, P = 0.05). Conclusion: The prognosis did not vary between the RCT and Cohort groups. H-containing regimens are often chosen for elderly patients with HER2-positive breast cancer. The prognosis of patients who received any H-containing regimen, even H monotherapy, was better than those who were not treated with H. Citation Format: Shinichi Baba, Masataka Sawaki, Yukari Uemura, Tsuyoshi Saito, Kokoro Kobayashi, Hiroaki Kawashima, Michiko Tsuneizumi, Noriko Sagawa, Hiroko Bando, Masato Takahashi, Miki Yamaguchi, Tsutomu Takashima, Takahiro Nakayama, Masahiro Kashiwaba, Toshiro Mizuno, Yutaka Yamamoto, Naruto Taira, Hiroji Iwata, Tatsuya Toyama, Koichiro Tsugawa, Yasuo Ohashi, Hirofumi Mukai. A cohort study to evaluate the efficacy and safety of postoperative adjuvant therapy in HER2-positive elderly breast cancer patients (RESPECT-cohort study) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-14-02.