BACKGROUND: Low-grade serous ovarian and peritoneal cancer (LGSC) is a rare disease and few data on the clinical and genomic landscape have been published.METHODS: A retrospective analysis of patients diagnosed with LGSC between 1996 and 2019 was conducted in MITO centers. Objective Response Rate (ORR) to treatments, progression-free survival (PFS) and overall survival (OS) were assessed. Additionally, the tumor molecular profile of 56 patients was evaluated using the Next Generation Sequencing (NGS) FoundationOne CDX (Foundation Medicine (R)).RESULTS: A total of 128 patients with complete clinical data and pathologically confirmed diagnosis of LGSC were identified. ORR to first and subsequent therapies were 23.7% and 33.7%, respectively. PFS was 43.9 months (95% CI:32.4-53.1) and OS was 105.4 months (95% CI: 82.7-not reached). The most common gene alterations were: KRAS (n = 12, 21%), CDKN2A/B (n = 11, 20%), NRAS (n = 8, 14%), FANCA (n = 8, 14%), NF1 (n = 7, 13%) and BRAF (n = 6, 11%). Unexpectedly, pathogenetic BRCA1 (n = 2, 4%), BRCA2 (n = 1, 2%) and PALB2 (n = 1, 2%) mutations were found.CONCLUSIONS: MITO 22 suggests that LGSC is an heterogenous disease for both its clinical behavior in response to standard therapies and its molecular alterations. Future prospective studies should test treatments according to biological and molecular tumor's characteristics

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