Differential presentation and outcome of sclerosing epithelioid fibrosarcoma (SEF) vs low grade fibromyxoid sarcoma (LGFMS): The nationwide series of 330 patients in NETSARC since 2010

Sclerosing Epithelioid Fibrosarcoma (SEF) and Low Grade Fibromyxoid Sarcoma (LGFMS) are ultrarare sarcomas (incidence 0.15 and 0.51/106/year respectively, PMID: 33630918) with close/similar translocations whose natural history and optimal treatment are not well known. We report on the nationwide exhaustive series of 330 patients with SEF or LGFMS in NETSARC+ since 2010. NETSARC (netsarc.org) is a network of 26 reference sarcoma centers with specialized multidisciplinary tumor boards (MDTB). Since 2010, pathological review is mandatory for sarcoma patients and patients’ characteristics are collected in the NETSARC+ nationwide database. The characteristics of patients with SEF and LGFMS and their outcome are presented and compared. 35/73 (47.9%) and 125/257(48,8%) of patients with SEF and LGFMS were female. More primary visceral, bone and trunk primary sites were observed in SEF (p<0.001). 30.1% of SEF vs 4.3% of LGFMS were metastatic at diagnosis (p<0.0001). Median size of the primary tumor was 51mm (range 10-90). For LGFMS vs 80mm (20-320) for SEF (p<0.001). Median age of LGFMS was 12 years younger than that of SEF (43 [range 4-98] vs 55 [range 10-91], p<0.001). Neoadjuvant treatment was more often given to SEF (16.4% vs 8.6%, p=0.05). More patients with LGFMS were operated first in reference centers (51% vs 26%, p<0.001).The R0 rate was 41% in LGFMS vs 16% in SEF (p<0.001). Median PFS of SEF and LGFMS were 32 and 136 months (p<0.0001) respectively. The median OS was not reached. 50-months OS was 92.6% vs 81% fr SEF (p=0.05). Median survival was 77 months after first relapse, similar for SEF and LGFMS. In multivariate analysis for PFS, SEF histotype, size of the tumor, met at diagnosis were independently correlated to survival. In multivariate analysis for OS, age, size of the tumor, met at diagnosis, but not SEF, independently correlated to survival. Although sharing close molecular alterations, SEF and LGFMS have a very different natural history, clinical presentation and outcome with a higher risk of metastatic relapse in SEF. Survival after relapse is longer than with other sarcomas, and similar for SEF and LGFMS.