P16-5 Single institute experience of treatment for metastatic HER2 positive breast cancer patients with trastuzumab deruxtecan

Abstract

Trastuzumab deruxtecan (T-DXd) is a robust drug conjugate for anti-HER2 therapy in metastatic breast cancer (MBC). In the DESTINIY-Breast01 study, the response rate was 60.9% and the common adverse events were a decrease neutrophil count, anemia, and nausea. The Interstitial lung disease (ILD) was seen in 13.6% of the patients, including 2.2% grade 5. T-DXd has been available since June 2020 in our daily practice, and now many MBC patients with HER2 positive have started T-DXd treatment. In this case series, we report the efficacy and safety of T-DXd among patients in our institute. We reviewed medical chart records of patients who underwent T-DXd between June 2020 and September 2020. The Granisetron and dexamethasone were used for antiemesis and for early detection of ILD, SpO2 and KL-6 is monitored on each visit. As of September 2020, there were fourteen HER2 positive MBC patients undergoing T-DXd as a treatment outside of a clinical trial. Median age was 61.5 years old (ranged 44 ∼ 79), all HER2 positive, 2 de novo stageIV and 12 MBC patients. Hormone receptor status was 5 ER- and PgR-, 9 ER+ and/or PgR+. Median treatment line was 4 (3 ∼ 12). Number of metastatic sites was median 2.5 organs, including 4 brain metastases, 7 lung, 3 liver, 9 bone, 7 lymph node and 4 local skin lesion, data overlapped. After two to four cycles of T-DXd treatment, each patient was assessed radiologically and/or by physical examination for the efficacy. One patient dropped out from follow up, two patients have just started the treatment and too early for the first assessment. Among eleven assessable patients, five patients achieved partial response (PR), six patients were in stable disease (SD) and there was no complete response (CR). As of September 2020, we have not experienced any severe adverse event due to the treatment nor ILD. T-DXd has been used amongst HER2 positive MBC patients effectively and safely without any severe AE.