Relay Therapeutics received Breakthrough Therapy Designation (BTD) from the US Food and Drug Administration (FDA) for zovegalisib (RLY-2608) in combination with fulvestrant.[1][3][4] This designation applies to adult patients with PIK3CA-mutated, HR+/HER2- locally advanced or metastatic breast cancer that has relapsed or progressed after treatment with a CDK4/6 inhibitor.[1][2][3] The BTD designation accelerates the development and review of drugs for serious diseases if early clinical data indicate a significant improvement over existing therapies.[3][4][5] Support came from phase 1/2 clinical data from the ReDiscover trial, which evaluated zovegalisib with fulvestrant.[2][4] Data included all PIK3CA mutations at doses of 600 mg BID fasted and 400 mg BID with food, the latter dose being used in the ongoing phase 3 ReDiscover-2 trial.[4] Initial phase 1/2 data for 400 mg BID with food in patients with prior CDK4/6 therapy will be presented March 16 at the ESMO Targeted Anticancer Therapies Congress.[2][4] Approximately 40% of patients with HR+/HER2- advanced breast cancer have PIK3CA mutations, and the majority experience recurrence or progression after CDK4/6 inhibitors.[4]