(P 139) ULTRA-RARE SARCOMAS HAVE WORSE SURVIVAL COMPARED TO NON-ULTRA-RARE SARCOMAS: A NATIONAL CANCER REGISTRY STUDY

Objective: Our understanding of the clinical characteristics, survival rate, and prognostic factors of ultra-rare sarcomas (URSs) is limited due to the low incidence. The aim of this study is to understand the clinical differences among URS, non-URS (NURS), and other non-sarcoma solid tumors (NSST).

Methods: Clinical demographics and survival of solid tumor patients(pts) of Taiwan Cancer Registry diagnosed between January 1, 2002, and December 31, 2019, were retrieved. URS included sarcoma histologies with an incidence < 1/1,000,000 persons. The annual percent change (APC) was computed to summarize the change in incidence for the recent years. Overall survival (OS) was estimated from the time of diagnosis to death or the last follow-up. The impact of gender, age, diagnosis period (2002-2010 vs. 2011-2019), and histology type on OS were estimated by Cox proportional hazard method.

Results: A total of 1,578,049 pts were included (URS [n=2,154], NURS [n=32,454], and NSST [n=1,543,441]). Among all sarcoma pts, 6.2% were URS; the top three most common histologies of URS were endometrial stromal sarcoma (n=292), pleomorphic liposarcoma (n=212), and epithelioid sarcoma (n=209). The APC of URS continued a surging trend from 2002 to 2019 (APC 3.81, p < 0.05) while the APC of NURS and NSST decelerated after 2010. URS pts are younger (p < 0.001) and more likely to be female (p < 0.001). In the multivariate analysis adjusted for gender, age, and diagnosis period, URS pts had worse OS than NURS pts (HR 1.70, 95% CI 1.59-1.81, p < 0.001). When all pts were divided into four age groups (0-18, 18-40, 40-70, and >70), the negative impact of URS on OS was most significant in adolescents and young adults (AYA, age 18-40) (HR:2.23; 95% CI, 1.94-2.55; p < 0.001). Unlike NSST, where the OS improved in the past decade (HR:0.84, 95% CI, 0.83-0.84, p < 0.001), OS of URS and NURS both worsened (URS: HR:1.14, 95% CI, 1.01-1.30; p < 0.05; NURS: HR:1.05, 95% CI, 1.02-1.09, p < 0.005) in the period 2011 to 2019 compared to 2002 to 2010.

Conclusion: Our findings showed that the incidence of URS is increasing but the OS worsened. Among different age groups, the detrimental effect of URS was most prominent in the AYA pts. Awareness of URS and precision medicine-based therapies for URS are desperately needed.