Inclusion Criteria:
* Histologically or cytologically documented locally advanced or metastatic solid tumour(s) of non-small cell lung cancer, ovarian cancer, endometrial cancer, breast cancer or prostate cancer at Screening.
* Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1 with no deterioration over the 2 weeks prior to dosing.
* Ability to swallow and retain oral medication.
* Minimum life expectancy ≥ 12 weeks in the opinion of the Investigator.
* Adequate organ and marrow function during Screening.
* Body weight \> 30 kg and no cancer-associated cachexia.
* Contraceptive use by participants or participant partners should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
Exclusion Criteria:
* Diagnosis of ataxia telangiectasia (ATR).
* History of another primary malignancy except for:
1. Malignancy treated with curative intent and with no known active disease ≥ 5 years before the first dose of the study intervention and of low potential risk for recurrence.
2. Basal cell carcinoma of the skin.
3. Curatively treated in situ cancer of the cervix.
4. Ductal carcinoma in situ.
5. Curatively treated lymphomas (without bone marrow involvement).
6. Squamous cell carcinoma of the skin or lentigo maligna that has undergone potentially curative therapy.
7. Adequately treated carcinoma in situ without evidence of disease.
* History of leptomeningeal carcinomatosis.
* History of myelodysplastic syndromes (MDS)/acute myeloid leukaemia (AML) or with features suggestive of MDS/AML (as determined by prior diagnostic investigation).
* Major surgical procedure (excluding placement of vascular access) or significant traumatic injury within 4 weeks of the first dose of study intervention.
* Spinal cord compression or brain metastases for at least 4 weeks prior to start of study intervention unless asymptomatic and stable.
* Persistent toxicities, with the exception of alopecia and vitiligo, caused by previous anti-cancer therapy.
* Participants with any known predisposition to bleeding.
* Refractory nausea and vomiting, chronic gastrointestinal diseases associated with diarrhoea, or previous significant bowel resection, with clinically significant sequelae that would preclude adequate absorption of ceralasertib.
* Any of the following cardiac criteria or cardiovascular diseases -
1. Any clinically important abnormalities in rhythm, conduction, or morphology of resting ECG.
2. Any factors that increase the risk of arrhythmic events such as heart failure, hypokalaemia, congenital long QT syndrome, family history of long QT syndrome, or unexplained sudden death under 40 years of age.
3. Participants at risk of brain perfusion problems.
4. Participants with relative hypotension or uncontrolled hypertension requiring clinical intervention.
5. Hypertensive heart disease with significant left ventricular hypertrophy or clinically significant valvular heart disease.
6. History of atrial or ventricular arrhythmia requiring treatment.
7. Transient ischaemic attack or stroke within 6 months prior to Screening.
* Any participant with active infection requiring systemic antibiotics, antifungal or antiviral drugs.
* Participants with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or active infection requiring systemic antibiotics, antifungal or antiviral drugs.
* Any prior treatment with an ATR inhibitor or checkpoint kinase inhibitor.
* Any concomitant treatment of central nervous system depressants, opioids, and centrally acting anti-hypertensive agents.
* Receipt of the last dose anti-cancer therapy within 4 weeks or 5 half-lives prior to the first dose of ceralasertib, whichever is shorter.
* Concomitant use of proton pump inhibitors, histamine H2 receptor antagonists, and other anti-acid agents.
* Palliative radiotherapy with a limited field of radiation within 2 weeks.
* Receiving or intend to receive any prescription or non-prescription drugs within 7 days or 5 half-lives before first dose of study intervention.
* Use of tobacco- or nicotine-containing products within 3 months prior to check-in or history of drug or alcohol abuse.
