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Background: Five-year survival rates for those diagnosed with soft tissue sarcoma (STS) have improved significantly among children and older adults (OAs), but these same trends have not been observed for adolescents and young adults (AYAs). While these disparities could be due to differences in biology or treatment, few studies have evaluated STS occurrence and outcome in AYAs. Therefore, the purpose of this study was to evaluate differences between adolescents and young adults (AYAs) and older adults (OAs) diagnosed with STS by stratifying analysis by: (1) clinical presentation; (2) treatment; and (3) survival.

Methods: Data were obtained from the Scandinavian Sarcoma Group (SSG) Central Register, which includes information on 5,747 patients from Sweden and Norway, diagnosed with a STS during 1986-2011. Variables included: age at diagnosis, metastasis at diagnosis, tumor size, histology, adjuvant treatment, date of death or last follow-up. AYAs were defined as those diagnosed ages 15-39 years. Categorical variables were analyzed using chi-square tests, and continuous variables were analyzed using t-tests. Overall survival (OS) and recurrence-free survival (RFS) were compared between AYAs and OAs using Kaplan-Meier estimates and log-rank tests. All analyses were conducted overall and by common STS subtypes.

Results: Overall and by STS subtype, there were significant differences between AYAs and OAs on presentation, treatment, and survival. The distribution of STS subtypes was different between OAs and AYAs. For example, OAs were more likely to be diagnosed with leiomyosarcoma compared to AYAs (18% vs. 10%, p<0.001), whereas AYAs were more likely to be diagnosed with malignant peripheral nerve sheath tumor (MPNST, 9% vs. 4%, p<0.001). OAs were also more likely to have larger tumors (>5 cm, 67% vs. 52%, p<0.001) and higher malignancy grade (grade IV, 45% vs. 31%, p<0.001). Interestingly, AYAs were more likely to be treated with radiotherapy and chemotherapy compared to OAs (12% vs. 5%, p<0.001). There were also differences within STS subtypes. For example, OAs were more likely to have metastasis compared to AYAs if diagnosed with leiomyosarcoma (18% vs. 10%, p=0.04). In most scenarios AYAs had significantly better OS and RFS compared to OAs, other than for MPNST (OS: p=0.19, RFS: p=0.28).

Conclusions: There were several differences between AYAs and OAs on STS presentation, treatment, and outcome. AYAs not only had differences in terms of STS subtypes but also tumor size and malignancy grade within subtypes. Additional work is needed to characterize the biology underlying these differences, which will inform future treatment strategies for both AYAs and OAs with STS.