Sarcomas developed in patients with Lynch Syndrome are enriched in pleomorphic soft-tissue sarcomas and are sensitive...

Sarcomas do not belong to the Lynch Syndrome (LS)-tumour spectrum. A growing body literature has reported sarcomas in patients with LS. Clinical and tumour characteristics of these patients remain unknown.

We set up the first national retrospective study, SarcLynch, describing the pathological and clinical characteristics of sarcomas developed in patients with LS. Patients were identified from two national networks and included from 23 centres in France.

Eighty-one patients participated in the SarcLynch study. Sixty-seven (83 %) tumours were soft-tissue sarcomas (STS) and 14 (17 %) bone sarcomas. Among STS, 59 (88 %) showed a pleomorphic component, with undifferentiated pleomorphic sarcoma (UPS) (36 %) and pleomorphic rhabdomyosarcoma (pRMS) (21 %) being the most represented subtypes. Sarcoma was the first neoplastic event in 32 patients (40 %). Thirty-two patients (40 %) were carriers of MSH2 germline pathogenic variants. Among patients who underwent an assessment of deficient mismatch repair (dMMR) by immunohistochemistry and/or molecular biology status, 75 % were dMMR by immunohistochemistry and 45 % were microsatellite instability high (MSI-H). Eight patients received immune checkpoint inhibitors and 4 (50 %) exhibited an objective response with 3 complete radiological response including 1 patient with pathological complete response. Duration of response ranged from 6 to 20 months.

SarcLynch, the largest multicentric series describing sarcomas developed in patients with LS, revealed an enrichment in patients with pleomorphic sarcomas - especially UPS and pRMS. This finding strongly supports screening for MMR status evaluation in these rare histotypes both for oncogenetic screening and therapeutic interest. Considering an objective response rate of 50 %, access to immunotherapy should be considered in these tumours.