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Orally Bioavailable SERD Shows Promise in Certain Breast Cancer Patients

A first-in-human, Phase I study is exploring D-0502 in women with advanced or metastatic HR-positive and HER2-negative breast cancer. This orally bioavailable selective estrogen receptor degrader (SERD) is well-tolerated with no dose-limiting toxicities observed, according to data presented at the 2020 San Antonio Breast Cancer Symposium (Abstract PS11-26). “Currently, fulvestrant is the only SERD approved for the treatment of advanced HR-positive breast cancer. It requires IM injection and has low bioavailability,” noted study author Cynthia Osborne, MD, with Texas Oncology-Baylor Charles A. Sammons Cancer Center. “This Phase I study is evaluating the drug D-0502, an oral bioavailable SERD. In preclinical models, it has demonstrated significant activity in a number of HR+ breast cancer models, including those with ESR1 mutations.” The aim of this Phase I study is to characterize the safety and tolerability of D-0502 alone and in combination with palbociclib, as well as to identify a maximum tolerated dose (MTD) and/or recommended Phase II dose. Secondary objectives included the evaluation of PK properties and preliminary anti-tumor activities. D-0502 was administered orally once daily in 28-day cycles. In the Phase Ia portion of the study, a standard 3+3 dose-escalation was used to identify the MTD of D-0502 as a single agent. The Phase Ib study, which is ongoing, includes two stages. “In stage I, D-0502 was evaluated with palbociclib at a dose below the MTD first before escalating to the MTD. Stage I also included patients in China treated at a dose below and at the MTD as a single agent, as well as in combination with palbociclib,” the study authors