Characterizing uveal melanoma patients with peritoneal metastases: a retrospective single-center analysis

BACKGROUND: Metastatic uveal melanoma (mUM) is an aggressive cancer predominately affecting the liver. Peritoneal metastases (PM) occur rarely, and there is limited knowledge about this subgroup´s clinical course and biology. METHODS: We analyzed 41 mUM patients with confirmed PM from the Charité-Universitätsmedizin Berlin database, focusing on clinical characteristics, immune cell infiltrates, genetic alterations and tumor mutational burden (TMB). RESULTS: The incidence of PM in mUM was 4.27 %. Metastatic disease was diagnosed 3.6 years after primary UM, with PM developing later (median: 4.7 years). Median overall survival (OS) from mUM diagnosis was 22.4 months. Prognosis correlated with metastatic pattern. Patients presenting with synchronous liver and peritoneal metastases or primary hepatic metastases followed by secondary peritoneal dissemination showed a median OS of 19.7 and 17.7 months, respectively. However, PM patients with exclusive extrahepatic disease at diagnosis of mUM had a significantly longer OS of 48.6 months and this metastatic pattern showed highly significant correlation with low and intermediate genetic risk. Metastasis-free survival and OS upon mUM diagnosis were significantly shorter in patients with high-risk UM tumors. TMB also correlated with metastatic pattern, being lowest in patients presenting with only extrahepatic disease. Higher TMB was generally associated with shorter OS. CONCLUSION: PM in mUM patients is rare and in contrast to other extra-abdominal tumors does not worsen prognosis. Prognosis is greatly influenced by the metastatic pattern, which is determined by tumor biology, as evidenced by its correlation with genetic risk groups and TMB.