Letrozole for Estrogen/Progesterone Receptor Positive Low-grade Serous Epithelial Ovarian Cancer (LEPRE Trial)

Primary objective: To determine if letrozole is superior to standard chemotherapy in terms of progression-free survival (PFS) in the first line treatment of patients with advanced low-grade serous epithelial ovarian carcinoma positive for estrogen and/or progesterone receptors. Secondary objectives: * to evaluate the response of tumor to letrozole compared with standard chemotherapy in terms of objective response rate (ORR); * to test the predictive effect of ER and PgR on response to letrozole in terms of PFS and ORR; * to evaluate the possible negative association between the effect of letrozole, in terms of PFS and ORR, and the proliferative index Ki67; * to evaluate the impact of letrozole compared with the impact of standard chemotherapy on patients' health related quality of life evaluated by Menopausal Quality of Life Questionnaire (MENQOL); * to evaluate the impact of letrozole compared with standard chemotherapy on patients' musculoskeletal pain evaluated by Brief Pain Inventory - Short Form (BPISF); * to evaluate the effect on overall survival (OS). As most patients will recur and will be switched to chemotherapy and vice versa, OS is not expected to be significantly different; * to evaluate the safety of letrozole compared with standard chemotherapy according to CTCAE v 5.0. Translational objectives: * to characterize the mutational profile and gene expression of the disease by NGS (next-generation sequencing) methodology on tissue samples; * to evaluate the circulating tumor DNA (ctDNA) on liquid biopsies as a tool to monitor the disease response.