Infantile versus adult-type fibrosarcoma and the risk of multiple primary malignancies: a retrospective cohort based on SEER database 2000-2021.

Background: Fibrosarcoma is a rare malignant neoplasm representing 10% of musculoskeletal sarcomas. It is classified as adult-type and infantile fibrosarcoma (IFS). Second primary malignancies (SPMs) may occur in fibrosarcoma survivors. As there are no studies that have analyzed this issue, we aimed to assess the risk of SPMs following fibrosarcoma diagnosis. Methods: Patients diagnosed with fibrosarcoma from 2000 to 2021 were selected using SEER*stat software. We used an MP-SIR session to calculate the standardized incidence ratio (SIR) as Observed/Expected (O/E), and the excess risk (ER) was per 10 000. Patients were subgrouped histologically: IFS, fibromyxosarcoma, periosteal fibrosarcoma, facial fibrosarcoma, dermatofibrosarcoma (DFS), central odontogenic fibrosarcoma, and ameloblastic fibrosarcoma. Results: Of 10 420 fibrosarcoma patients, 1048 developed SPMs. The majority were Caucasians (71.1%), and 50.2% were females. A significant risk of SPMs was observed in all sites (O/E = 1.46, P < 0.05, ER = 35.21). IFS had no risk to develop SPMs (Observed = 1.00, O/E = 1.85, P > 0.05). DFS had a high SPMs risk (O/E = 1.52, P < 0.05, 95% CI: 1.41-1.64). Fibromyxosarcoma SPMs had an alarming risk if they originated in the heart and soft tissue (O/E = 32.38, P < 0.05, 95% CI: 23.2-43.9). Conclusions: There is a significantly high risk of multisystem SPMs following primary fibrosarcoma, especially for Caucasians and females. IFS had an insignificant risk of SPMs compared to adult-type fibrosarcomas (AFS). The common sites for SPMs were the heart and soft tissue. The results highlight the necessity of SPMs screening after AFS diagnosis.