Ovarian cancer is among the top five primary causes of cancer-related mortality in women. Most ovarian malignant tumours originate from epithelial cells The majority of patients typically have advanced-stage tumours at diagnosis. When complete surgery with no macroscopic visible disease is not feasible due to both the spread of the disease and the patient's general condition, neoadjuvant chemotherapy (NACT) of 3 cycles followed by interval cytoreductive surgery (ICS) or final cytoreductive surgery (FCS) after 6 cycles of NACT followed or not by adjuvant chemotherapy can be offered, with similar overall survival. In our centre, due to logistics, disease, or patient factors, many patients may receive more than 3 cycles of NACT before ICS. Therefore, this randomized controlled trial aims to evaluate the survival benefit of different timings of ICS after 3 or 6 cycles of NACT in patients not eligible for upfront cytoreductive surgery (UCS).