Insights into Non‐Classic Primary Bone Sarcomas in Children, Adolescents, and Young Adults: A French Descriptive Study

Background Bone sarcomas other than osteosarcoma, chondrosarcoma, and Ewing sarcoma represent a challenge in care because they are uncommon, especially in children, adolescents, and young adults (AYA). Methods We conducted a retrospective review of patients aged 0–25 years treated for non‐osteosarcoma, non‐chondrosarcoma, non‐Ewing (and related) primary bone sarcomas in France between 2011 and 2021. Patients were identified through the French databases: ResOs and Conticabase. Results Forty‐nine patients treated in 18 centers were analyzed. The median age was 15 years (3.0–25.0), and the male/female ratio was 0.58. The median follow‐up was 33.9 months (IQR: 15.0–63.7). Twenty‐three patients (46.9%) were diagnosed with adamantinomas, eight (16.3%) with chordomas, 15 (30.6%) with undifferentiated sarcomas, two (4.1%) with leiomyosarcomas, and one (2.0%) with angiosarcoma. Adamantinomas were treated by surgery, and chordomas by surgery and/or radiotherapy. High‐grade tumors composed of undifferentiated sarcomas, leiomyosarcomas, and angiosarcomas were treated with an association of chemotherapy, surgery, and radiotherapy. None of the patients with adamantinoma relapsed. Half of the patients with chordoma relapsed without any deaths. The 5‐year overall survival and progression‐free survival rates for patients with high‐grade tumors were 44.4% (95% CI: 14.9%–70.7%) and 37.5% (95% CI: 16.1%–59.1%), respectively. Conclusion Non‐classic primary bone sarcomas in children and AYA are extremely rare. Adamantinomas have an excellent outcome. Chordomas exhibit local aggressiveness and high recurrence rates, with a need to improve local control and systemic treatments. Other tumors are mainly undifferentiated sarcomas and have a poor prognosis, and no consensus as to adequate systemic treatment.