Rain Therapeutics Inc. announced its plan to commence a phase 2 clinical trial, named MANTRA-3, evaluating the efficacy of milademetan, an oral mouse double minute 2 (MDM2) inhibitor, as a monotherapy for the treatment of patients with Merkel cell carcinoma (MCC) refractory to immune checkpoint inhibition (ICI) in mid-2022. Recent data presentations at the 2021 AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics demonstrated potent in vitro and in vivo activity of milademetan in several MCC models. The company will prioritize its financial resources towards a phase 2 clinical trial of milademetan in MCC and replace the previously planned phase 2 clinical trial of milademetan in intimal sarcoma. The MANTRA-3 trial is designed to evaluate the efficacy of milademetan as a monotherapy in patients with MCC that have progressed on immune checkpoint inhibitors. Approximately 30 patients are expected to be enrolled to receive milademetan. The primary endpoint of the trial is objective response rate (ORR) as measured by RECIST criteria. Secondary endpoints include duration of response, disease control rate, progression free survival by investigator assessment, growth modulation index, overall survival and safety.