MAintenance Therapy With Aromatase Inhibitor in Epithelial Ovarian Cancer (MATAO)

Inclusion Criteria: * Patients must be ≥ 18 years of age * Willing and able to attend the visits and to understand all study-related procedures. * Primary, newly diagnosed FIGO Stage II to IV and histologically confirmed low or high grade serous or endometrioid epithelial ovarian/fallopian tube/peritoneal cancer * (Interval-) debulking performed ECOG-Performance Status 0-2 * Signed informed consents (ICF-1; ICF-2) * Paraffin-embedded tissue or paraffin-embedded cell block (from ascites) available * Positivity (≥ 1%) for ER expression (only determined by Histopathology Core Facility of MATAO trial) * At least 4 cycles of platinum-based chemotherapy (neoadjuvant allowed) * Negative serum pregnancy test in women of childbearing potential who will get/have gotten a surgical resection or radiation sterilization, prior to the intervention in the therapeutical maintenance setting. Exclusion Criteria: * Progressive disease at the end of adjuvant treatment as defined in chapter 9.2.1 of protocol * Women of childbearing potential (not having undergone a surgical or radiation sterilization and not getting a surgical resection, prior to the intervention in the therapeutical maintenance setting) * Pregnant or lactating women * Any other malignancy within the last 5 years which has impact on the prognosis of the patient * \< 4 cycles of chemotherapy in total * Contraindications to endocrine therapy * Inability or unwillingness to swallow tablets * Patients with a known intolerance to galactose, lactase deficiency and glucose-galactose malabsorption