Daiichi Sankyo Presents Updated Phase 1 Results of [Fam-] Trastuzumab Deruxtecan (DS-8201) in Patients with HER2 Low Expressing Metastatic Breast Cancer at 2018 San Antonio Breast Cancer Symposium (SABCS)

- Updated analysis from ongoing phase 1 study of [fam-] trastuzumab deruxtecan (DS-8201) demonstrated a confirmed overall response rate of 44.2 percent and a disease control rate of 79.1 percent in 43 evaluable patients with heavily pretreated HER2 low metastatic breast cancer

- A further subgroup analysis of 38 patients whose disease was also hormone receptor (HR) positive showed a 47.4 percent confirmed overall response rate and 81.6 percent disease control rate

- No anti-HER2 therapies are currently approved for HER2 low expressing breast cancer, and plans for a phase 3 study are underway

TOKYO and MUNICH and BASKING RIDGE, New Jersey, Dec. 8, 2018 /PRNewswire/ -- Daiichi Sankyo Company, Limited (hereafter, Daiichi Sankyo) announced that updated safety and efficacy data from the ongoing phase 1 study with [fam-] trastuzumab deruxtecan, an investigational HER2 targeting antibody drug conjugate (ADC), were presented for a subgroup of patients with heavily pretreated HER2 low expressing metastatic breast cancer during a Poster Session at the 2018 San Antonio Breast Cancer Symposium (SABCS) (#P6-17-02).

The updated analysis of 43 evaluable patients with HER2 low expressing metastatic breast cancer (IHC 2+/ISH- or IHC 1+), who received [fam-] trastuzumab deruxtecan at a recommended expansion dose of 5.4 or 6.4 mg/kg, demonstrated a confirmed overall response rate of 44.2 percent (19/43 patients) and a disease control rate of 79.1 percent (34/43 patients). Preliminary estimate of median duration of response was 9.4 months (range: 1.5+, 23.6+), and median progression-free survival was 7.6 months (95 percent CI: 4.9, 13.7). A total of 54 patients with heavily pretreated (median 7.5 prior anticancer regimens) HER2 low breast cancer have received ≥1 dose [fam-] trastuzumab deruxtecan 5.4 or 6.4 mg/kg in the study and 23 patients remain on treatment as of data cut-off on October 12, 2018.

"While anti-HER2 therapies play an important role in the treatment of HER2 positive breast cancer, they historically have not demonstrated effectiveness against tumors that express lower levels of HER2," said Shanu Modi, MD, Breast Medical Oncologist, Memorial Sloan Kettering Cancer Center and study investigator. "These data offer preliminary evidence of [fam-] trastuzumab deruxtecan activity in HER2 low expressing breast cancers, and based on further study, we are beginning to consider the implications for how we classify and treat these patients."