Study evaluating the efficacy of:

INTERVENTION: Interventional Treatment: Drugs ‐ Olaparib is a PARP inhibitor, targeting DNA repair processes. Treatment: Drugs ‐ Cyclophosphamide is a chemotherapy that has been used for the treatment of ovarian cancers for many years. Treatment: Drugs ‐ Durvalumab is a PD‐L1 inhibitor, an antibody (a type of human protein) that works by blocking a body substance called PD‐L1. Blocking (inhibiting) PD‐L1 helps the body’s immune system to attack cancer cells. Patients will be randomised to: A) Olaparib tablets 300mg orally twice daily for 12 weeks, followed in the absence of progression according to RECIST 1.1 by olaparib 300 mg twice daily plus durvalumab 1500mg IV every 4 weeks for 12 cycles, followed by olaparib alone until progression; B) Olaparib 300mg twice daily plus oral cyclophosphamide 50mg daily for 5 out of 7 days a week (1000mg per 4 weeks), for 3 x four‐weekly cycles over 12 weeks, followed in the absence of progression according to RECIST 1.1 by olaparib plus durvalumab (dosing schedule as above) for 12 cycles, followed by olaparib alone until progression; C) Olaparib 300mg twice daily until progression. Participant compliance with olaparib and cyclophosphamide will be determined at each clinic visit by reviewing patient diaries. CONDITION: Fallopian tube cancer Ovarian cancer Peritoneal cancer PRIMARY OUTCOME: To determine in each treatment arm: ; 1) 36 week progression‐free survival rate (36wPFS, death or PD by RECIST 1.1 criteria at 36 weeks) ; SECONDARY OUTCOME: Aspects of health related quality of life (EORTC QLQ‐C30, OV28 and MOST) Exploratory assessment of ctDNA in available plasma samples. Frequency and severity of adverse events (CTCAE v4.03) ‐ composite outcome. ; Examples may include: Drug toxicity, drug adverse reactions etc. Number of responders to PARPi and/or LDCy combination and/or immune therapy determined using a Cyclophosphamide‐UPregulation (CUP) test. ; ; Objective response (OR = CR or PR) rate (ORR) by RECIST 1.1 or GCIG CA125 criteria. Objective response rate (ORR) is defined as the proportion of patients experiencing a complete response (CR) or partial response (PR) by RECIST 1.1 or GCIG CA125 criteria. Objective tumour response (OTR = CR or PR) rate (OTRR) and PFS by iRECIST. Objective tumour response rate (OTRR) in each arm is defined as the proportion of participants with an objective tumour response (OTR = CR + PR) divided by the total number of participants with measurable disease at baseline in that cohort. Progression free survival (PFS) by RECIST 1.1 or GCIG CA125 criteria. Time to development of symptoms associated with progression, specifically abdominal/gastrointestinal symptoms including: abdominal pain/discomfort/cramps; changes in bowel habits; indigestion/heartburn; nausea; vomiting; bloating. ; This outcome will be assessed by review of patient completed questionnaires including EORTC QLQ‐C30, OV28 and MOST. Time to starting first subsequent therapy (TFST) or death. INCLUSION CRITERIA: 1. Women, aged 18 years and older, with histologically confirmed high‐grade serous carcinoma of the ovary, fallopian tube or primary peritoneum. 2. Undergone adequate debulking surgery and 1 line of platinum‐based chemotherapy. Patients who received bevacizumab as part of first‐line treatment are eligible. 3. Known germline BRCA1 and BRCA2 status. Both BRCA mutant and BRCA wild‐type patients are eligible. For patients who are BRCA wild‐type, they must have: • Initial diagnosis of high‐grade serous carcinoma at less than 70 years of age; • Normalisation of CA125 to less than upper limit of normal (ULN) by the end of cycle 4 of first‐line chemotherapy. 5. Patients can have either RECIST measurable or non‐measurable disease o 4. First CA125 GCIG progression after first‐line treatment, occurring 6 months or more following the last dose of chemotherapy, defined as CA125 readings twice the upper limit of normal on 2 occasions at least 1 week apart.