Purpose: This study was performed to determine the incidence and risk factors involved in the development of a second malignant neoplasm (SMN) after treatment of primary rhabdomyosarcoma (RMS) in patients enrolled onto Intergroup Rhabdomyosarcoma Studies I and II (IRS I and II).
Patients and methods: There were 1,770 patients with primary RMS entered onto IRS I and II between 1972 and 1984. They were treated with chemotherapy and, in most instances, radiotherapy according to randomized or assigned regimens based on clinical grouping. Median follow-up time for these patients was 8.4 years. Incidence density (ID) was calculated for each study and for treatment and age groups. The 10-year cumulative incidence was estimated for each study.
Results: Twenty-two SMNs have been reported through 1991. The most common tumor type was a bone sarcoma followed by acute nonlymphoblastic leukemia (ANLL). The median time to the development of an SMN was 7 years (range, 1 11/12 to 15 9/12 years). The 10-year cumulative incidence rate was 1.7% for both studies. ID and cumulative incidence estimates were highest for patients who received both an alkylating agent and radiotherapy. The majority of patients for whom family histories were available had either neurofibromatosis themselves or a family history that suggested the Li-Fraumeni syndrome (LFS).
Conclusion: The results of this study suggest that genetic abnormalities play a prominent role in the development of an SMN after therapy for a primary RMS. Chemotherapy with an alkylating agent and radiotherapy play significant roles in the development of an SMN compared with patients who received only one of these therapeutic modalities.