Abstract PS11-39: Phase II pilot study of trastuzumab biosimilar (herzuma®) plus gedatolisib in patients with HER-2 positive metastatic breast cancer who progressed after 2 or more HER-2 directed chemotherapy [KM-10A/KCSG18-13 interim analysis

Abstract

Abstract Background: Prognosis of patients with HER-2 positive metastatic breast cancer (MBC) has been revolutionized with the development of dual antibodies targeting HER-2 and antibody-drug conjugate, but resistance to anti-HER-2 therapy is inevitable ultimately. PI3K-AKT-mTOR pathway aberration is known to be one of the resistance mechanisms. This randomized phase 2 pilot study evaluated safety and efficacy of Herzuma® (trastuzumab biosimilar) plus Gedatolisib (dual PI3K/mTORC inhibitor) in patients with HER-2 positive MBC who progressed after multiple lines of therapy. Methods: Patients with HER-2 positive MBC with known PIK3CA pathologic mutation or amplification whose disease progressed after more than two HER-2 directed therapy were enrolled in the study. They received Herzuma® (8mg/kg IV for 1st cycle loading dose, and then 6mg/kg IV every 3 weeks) plus Gedatolisib (180mg on D1, 8, 15 of every 21 days). We evaluated efficacy of the combination treatment as interim analysis. The data cutoff of this interim analysis was Aug 4, 2020. Results: As a pilot study, 15 patients were enrolled and followed for a median of 2.3 months. At data cutoff, 11 patients were eligible for response assessment. All patients were confirmed to have pathologic PIK3CA aberrations: H1047R, H1047L, E542Q, E542K, E453K, N345K, and PIK3CA amplification. Five patients reached partial response (PR) as their best response, three were stable disease (SD), and three had progressive disease (PD). All patients who have reached PR remain on investigational treatment at the data cutoff point, and the longest one is on treatment for 7.8 months. One of the SD patients ended treatment due to disease progression, and the other two have been undergoing treatment. Overall, response rate was 45.5% and disease control rate was 72.7%. No fatal adverse events related to trial medication were reported. Conclusion: In this phase 2 pilot study, Trastuzumab biosimilar plus Gedatolisib presented 45.5% of response rate with manageable toxicity in patients with HER-2 positive MBC with PIK3CA aberration. Clinical trial information: NCT03698383 Acknowledgement: this research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health &Welfare, Republic of Korea (Grant number: HI17C2206). Citation Format: Ju Won Kim, Hee Kyung Ahn, Jong Gwon Choi, Yee Soo Chae, Gyeong Won Lee, Keon Uk Park, Eun Mi Lee, Sung Hoon Sim, Jee Hyun Kim, Yeon Hee Park, Mi So Kim, Jin Hyun Park, Jeong Eun Kim, Han Jo Kim, Mi Sun Ahn, So Yeon Oh, Min Hwan Kim, Su-Jin Koh, Kyoung Eun Lee, Myoung Joo Kang, Jae Ho Byun, Joo young Ha, Jung Hye Kwon, Joo Young Jung, Su Ee Lee, In Hae Park, Kyong Hwa Park. Phase II pilot study of trastuzumab biosimilar (herzuma®) plus gedatolisib in patients with HER-2 positive metastatic breast cancer who progressed after 2 or more HER-2 directed chemotherapy [KM-10A/KCSG18-13 interim analysis] [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS11-39.