Background: KIF18A is a mitotic kinesin motor protein that regulates chromosome positioning during cell division and is overexpressed in a subset of human cancers. TP53 mutant unstable aneuploid cancer cells with chromosomal instability (CIN) features are dependent on KIF18A motor activity to prevent lethal multipolar cell division. Preclinical data demonstrate that treatment with AMG 650; an oral, first in class, selective small molecule inhibitor of KIF18A may be safe and tolerable. We are conducting a first-in-human phase 1 study with AMG 650 in adult subjects with locally advanced or metastatic solid tumors with TP53MUT, triple negative breast cancer (TNBC), high grade serous ovarian cancer (HGSOC) or serous like endometrial cancers and other solid tumors. Methods: In this phase 1, multicentric, dose escalation and dose expansion study we evaluate the safety and tolerability of AMG 650 monotherapy in patients with advanced/metastatic solid tumors (NCT04293094). The main objective is to determine the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) based on emerging safety, efficacy, and pharmacodynamics (PD) data prior to reaching the MTD. Key inclusion criteria include the presence of measurable disease and diagnosis of advanced/metastatic triple negative breast cancer (TNBC), high-grade serous ovarian cancer (HGSOC), serous-like endometrial cancer or other solid tumors with documented TP53 mutations. In the dose expansion phase, participants with locally advanced or metastatic TNBC or HGSOC will be treated with the preliminary RP2D identified from the dose exploration part of the study. Primary endpoints include the incidence of Dose Limiting Toxicities (DLTs),Treatment-Emergent Adverse Events (TEAEs), Serious Adverse Events (SAEs), Treatment-related Adverse Events and the evaluation of the number of participants who experience a clinically significant change from baseline in vital signs, electrocardiogram and laboratory tests parameters. Secondary endpoints include Objective Response Rate, Duration of Response, Progression-free Survival, Clinical Benefit Rate, Time to Response, Time to Progression, Overall Survival (OS), Maximum Plasma Concentration (Cmax) of AMG 650, Time to Maximum Plasma Concentration (Tmax) of AMG 650 as well as Area Under the Plasma Concentration-time Curve (AUC) Over the Dosing Interval for AMG 650. Continuous monitoring of toxicity is conducted. The study began enrolling pts in March 2020 and is ongoing. For more information, please contact Amgen Medical Information: medinfo@amgen.comClinical trial information: NCT04293094