Osteosarcoma as a secondary malignancy following rhabdomyosarcoma: A report of 28 affected patients from the Cooperative Osteosarcoma Study Group (COSS)

Background Osteosarcoma may arise as a secondary malignancy following rhabdomyosarcoma (RMS). We utilized the Cooperative Osteosarcoma Study Group (COSS) database to better understand this association. Patients and methods The COSS database (1980‐05/2023) was searched for patients whose osteosarcoma was preceded by RMS. Eligible patients were analyzed for patient‐, tumor‐, and treatment‐related variables as well as outcomes. Results The search revealed 28 eligible osteosarcomas (27 high‐grade central, one periosteal; male:female = 16:12; median age RMS 2.1 [range: 0.9–10.0] years, osteosarcoma 13.5 [7.2–29.0] years). Genetic tumor‐predisposition syndromes were documented in 12 patients. One patient had had a distinct malignancy prior to RMS, two intermittently, seven following osteosarcoma. Local RMS treatment had included radiotherapy in 20/26 cases (two unknown). Secondary osteosarcoma sites were extremity 13, trunk seven, head and neck eight; 15 osteosarcomas were radiation‐associated. There was only one case of primary osteosarcoma metastases. Osteosarcoma treatment included chemotherapy (27), surgery (26), or radiotherapy (2). A macroscopically complete remission of all osteosarcoma sites was achieved in 24 cases. Median follow‐up was 5.8 (range: 0.5–18.4) years after osteosarcoma and 8.1 (1.0–15.4) years for 14 survivors. Actuarial 5‐year overall and event‐free survival were 66% (standard error 9%) and 45% (10%), respectively. Five of 14 deaths were caused by further malignancies. Conclusion This series offers a benchmark for patients who develop a secondary osteosarcoma after RMS. Affected patients are generally still in the pediatric age. The results obtained strongly argue for genetic predisposition testing in RMS and against therapeutic leniency in comparable situations.