This observational study aims to gather comprehensive data on primary ovarian leiomyosarcoma (POLMS). This extremely rare malignancy accounts for less than 3% of primary ovarian malignancies and has an incidence of only 1% among ovarian cancers. This national, retrospective and prospective multicenter study will collect and analyze historical cases of POLMS with remote diagnoses accessed through clinical case reviews and newly identified cases. The study aims to expand a previously identified series of 113 cases described in the literature, uncovering patterns in diagnosis, treatment, and outcomes and ultimately establishing evidence-based guidelines for the optimal management of this rare and aggressive cancer.