Trial of THEO-260 (Administered Via Intraperitoneal Route) in Ovarian Cancer Patients

* Inclusion Criteria: * Confirmed histological diagnosis of advanced high grade serous or endometrioid cancer of the fallopian tube, primary peritoneum or ovary either on archival biopsy or fresh tumour biopsy. * Platinum-resistant or refractory disease: platinum-resistance is defined as radiological progression within 6 months of last cycle of platinum treatment; platinum refractory disease is defined as radiological progression during the 3 months following the first dose with platinum treatment. * Life expectancy of \> 6 months. * ECOG performance status of 0 or 1. * Measurable disease as per RECIST V1.1. * No clinical history of bowel obstruction in past 3 months or no clinical signs or symptoms of bowel obstruction. Exclusion Criteria: * Prior anti-cancer treatment or Investigational Product within 28 days or 5 half-lives, prior to first dose of THEO-260. * Prior treatment with a group B adenovirus. * Radiation therapy within 4 weeks of first dose of THEO-260 * Clinical evidence of cerebral metastases or Central Nervous System (CNS) involvement including leptomeningeal disease. Patients with previous cerebral metastases must have no evidence of progression or haemorrhage after treatment. * Uncontrolled pleural effusion or pericardial effusion requiring recurrent drainage procedures (as defined as once monthly or more frequently). * Prior pneumonitis or history of interstitial lung disease. * Confirmed QTcF ≥470 ms on screening 12-lead ECG or history of Torsades de Pointes or history of congenital long QT syndrome. * Concomitant medications that prolong the QTc interval and/or increase the risk for Torsades de Pointes. * Patients with active hepatitis infection or hepatitis C. Patients with past hepatitis B virus (HBV) infection or resolved HBV infection are eligible. * Active infection with tuberculosis. * Active infection with severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2). * Patients with active human immunodeficiency virus (HIV) infection or known history of HIV infection. * Active infection requiring IV antibiotics within 2 weeks prior to first dose of THEO-260, or long-term oral therapy for systemic infection. * Known contra-indications or hypersensitivity to the excipients of THEO-260. * Active autoimmune disease that has required systemic treatment in the past 2 years. * Known heart failure New York Heart Association (NYHA) Class 2-4. * Known contra-indications or hypersensitivity to acetominophen. * Known alcohol consumption in excess of 2 units per day. * Left ventricular ejection fraction (LVEF) \<45%, unstable angina, serious uncontrolled cardiac arrhythmia, a myocardial infarction within 6 months prior to trial enrolment or a history of myocarditis. * Arterial oxygen saturation \<92% on room air prior to first dose of THEO-260. * Received any licensed or investigational vaccines within 30 days prior to Day 1