Study of ART0380 in Patients With Biologically Selected Solid Tumors

Inclusion Criteria: * Patients who have discontinued all previous treatments for cancer for at least 21 days or 5 half-lives (not including palliative radiotherapy at focal sites), whichever is shorter. Palliative radiotherapy must have completed 1 week prior to start of study treatment. * Resolution of all toxicities of prior therapy or surgical procedures to baseline or Grade 1 (except for hypothyroidism requiring medication, neuropathy, and alopecia, which must have resolved to Grade ≤2). * Have adequate organ function. * Patients of childbearing potential and patients with partners of childbearing potential are required to use highly effective contraception. * Have an estimated life expectancy of ≥12 weeks, in the judgment of the investigator. * Performance status of 0-1 on the Eastern Cooperative Oncology Group scale. * Have a non-irradiated tumor tissue sample (archival or newly obtained core biopsy of a tumor lesion) available. Inclusion Criteria specific to each Arm Inclusion Criteria for Arm 1 \[ART0380 monotherapy (endometrial cancer patients)\] * Persistent or recurrent EC with biological selection. * Patients should have received taxane/platinum chemotherapy unless contraindicated. * Measurable disease. Inclusion Criteria for Arm 2 \[ART0380 monotherapy (solid tumors patients)\] * Advanced or metastatic solid cancers of any histology with biological selection. * If a Programmed cell death protein-1 /Programmed death-ligand-1 inhibitor (e.g., pembrolizumab) is approved and available for the patient's cancer, the patient should have received such treatment before participating in this study. * Radiologically evaluable disease. Exclusion Criteria: * Patients who are pregnant. * Prior treatment with an inhibitor of ATR, WEE1, checkpoint kinase 1 or PKMYT1. * Have a serious concomitant systemic disorder that would compromise the patient's ability to adhere to the protocol. * Have ongoing interstitial lung disease or pneumonitis (whether symptomatic or asymptomatic). * Patients with treated brain metastases are eligible if follow-up brain imaging after central nervous system (CNS) directed therapy shows no evidence of progression. * Have any major gastrointestinal issues that could impact absorption of ART0380. * Have a history of allergy or hypersensitivity to study drug components. * Have a significant bleeding disorder or vasculitis or had a Grade ≥3 bleeding episode within 12 weeks prior to enrollment. * Patients who plan to father a child while in the study or within 16 weeks (5 months in France) after the last administration of study treatment.