Investigating Idetrexed and Olaparib in Patients With Ovarian Cancer

Inclusion Criteria: * Histologically or cytologically proven high grade serous ovarian cancer refractory to conventional treatment, or for which no conventional therapy exists or is declined by the patient. * Measurable (as defined by RECIST v1.1) or evaluable (based on tumour markers) disease. * Life expectancy of at least 12 weeks. * World Health Organisation (WHO) performance status of 0-1 (Appendix 1 of Protocol). * Haematological and biochemical indices within the ranges shown in Protocol section 4.1.1). These measurements must be performed within one week (Day -7 to Day 1) prior to the patient's first dose of IMP. Normal (no clinically significant abnormalities) 12-lead ECG, QTcF interval \<470 ms * Pulmonary function test FVC of \>70%, DLCOc (DLCO corrected for Hb) of \>60%. * 18 years or over. * Written (signed and dated) informed consent and be capable of co-operating with treatment and follow-up. * For dose expansion patients only, they must have medium to high α-folate receptor expression according to the Ventana FOLR1-2.1 IHC assay. Exclusion Criteria: * Radiotherapy (except for palliative reasons), endocrine therapy, immunotherapy or chemotherapy during the previous four weeks (six weeks for nitrosoureas, Mitomycin-C) and 4 weeks for investigational medicinal products) before treatment. * Ongoing toxic manifestations of previous treatments. Exceptions to this are alopecia or certain Grade 1 toxicities, which in the opinion of the Investigator and the DDU should not exclude the patient. * Patients with new brain metastases. Patients with treated (surgically excised or irradiated) and stable brain metastases are eligible as long as the treatment was at least 4 weeks prior to initiation of study drug and brain MRI within 2 weeks of initiation of study drug is negative for new metastases. * Patients with pulmonary metastases. * History of thoracic radiation or other history likely to create pre-existing lung disease * Presence of significant clinical ascites and/or pleural effusions. * Female patients of child-bearing potential (or are already pregnant or lactating). However, those patients who have a negative serum or urine pregnancy test before enrolment and agree to use two forms of contraception (one effective form plus a barrier method) \[oral, injected or implanted hormonal contraception and condom; intra-uterine device and condom; diaphragm with spermicidal gel and condom\] or agree to sexual abstinence (see Protocol Section 16.5 - Appendix 5), effective from signing the consent form, throughout the trial and for six months afterwards are considered eligible. * Major thoracic or abdominal surgery from which the patient has not yet recovered. * Patients with sub-acute bowel obstruction. * Organ transplant patients. * At high medical risk because of non-malignant systemic disease including active uncontrolled infection. * Known to be serologically positive for hepatitis B, hepatitis C or human immunodeficiency virus (HIV). * Patients with history of QT prolongation, clinically significant VT, VF, heart block, MI within 1 year, CHF NYHA Class III or IV, unstable angina, angina within 6 months, or other evidence of clinically significant coronary artery disease/ * Is a participant or plans to participate in another interventional clinical trial, whilst taking part in this Phase I/Ib study of Idetrexed and Olaparib. Participation in an observational trial would be acceptable. * Inability to tolerate Olaparib. * Any other condition which in the Investigator's opinion would not make the patient a good candidate for the clinical trial. * Confirmed, current COVID-19 infection.