The dose-finding, phase 1b/2 KRT-232-103 study (NCT03787602) evaluated navtemadlin in adult TP53WT MCC pts who failed anti-PD-1/L1 therapy. Evaluable pts receiving 180 mg 5D on/23D off showed a 25% confirmed ORR, a 38% unconfirmed + confirmed ORR, and a 63% disease control rate (Table); median duration of response was not reached (range, 6-16.2+ mo) and median time to treatment response was 4.1 mo (range, 1.2-7). Notably, one responder, following a prolonged partial response, achieved complete metabolic remission by PET/CT after 2 y on treatment. Navtemadlin is the first targeted agent to show promising single-agent activity in heavily pretreated MCC pts who failed anti-PD-1/L1 therapy.