Personalised Timing of Interval Debulking Surgery in Advanced Ovarian Cancer

Inclusion Criteria: 1. Patients must be at least 18 years old. 2. Patients who have Eastern Cooperative Oncology Group (ECOG) score 0-1. 3. Patients who are competent to give informed consent. 4. Patients who have stage III-IV histologically or cytologically confirmed epithelial ovarian cancer, fallopian tube or primary peritoneal cancer not amenable for primary debulking surgery (PDS). 5. Patients who are planned for neoadjuvant chemotherapy (NACT) using platinum-based chemotherapy +/- bevacizumab or biosimilar. Those who are receiving NACT before interval debulking surgery (IDS) are also eligible. 6. Patients who have an evaluable CA125 level at baseline (i.e., baseline level is at least 2x upper limit of normal). 7. Patients who have baseline computed tomography of at least abdomen and pelvis, or positron emission tomography (PET)-CT. Magnetic resonance imaging (MRI) is also acceptable but the same modality has to be used when assessing the feasibility of IDS. 8. Patients who agree to undergo IDS, where the time of IDS may differ from the usual clinical practice. 9. Patients who agree to receive adjuvant chemotherapy, if clinically indicated. The total number of chemotherapy should be at least four or above. Exclusion Criteria: 1. Patients who have borderline malignancy, or non-epithelial ovarian cancer like germ cell or sex cord tumor, or metastatic diseases from other origins like Krukenberg's tumor 2. Patients who are eligible for PDS 3. Patients who are not fit for PDS because of medical morbidities or refusal of operation 4. Patients who have already started NACT outside the study centres, except those who have just had one cycle within 21 days and the baseline CA125 is available. 5. Patients who are pregnant