Purpose: To simplify the recommended staging evaluation by correlating tumor and clinical features with patterns of distant metastasis in newly diagnosed patients with embryonal rhabdomyosarcoma (ERMS) or alveolar rhabdomyosarcoma (ARMS).
Patients and methods: Patient data from the Intergroup Rhabdomyosarcoma Study Group and the Children's Oncology Group over two periods were analyzed: 1991 to 1997 and 1999 to 2004. We used recursive partitioning analyses to identify factors (including histology, age, regional nodal and distant metastatic status, tumor size, local invasiveness, and primary site) that divided patients into subsets with the most different rates of metastatic disease.
Results: Of the 1,687 patients analyzed, 5.7% had lung metastases, 4.8% had bone involvement, and 6% had bone marrow (BM) involvement. Rhabdomyosarcoma (RMS) without local invasion (T1) had a low rate of metastasis for all distant sites, especially ERMS (0% bone, 0% BM). ARMS with local invasion (T2) had a higher rate of metastasis for all distant sites (13% lung, 18% bone, 23% BM). ERMS, T2 also had a higher rate of metastatic lung involvement (9%). The likelihood of bone or BM involvement increased in the presence of lung metastases (41% with, 6% without). Regional nodal metastases (N1) predicted a high rate of metastasis in all distant sites (14% lung, 14% bone, 18% BM). A staging algorithm was developed.
Conclusion: Staging studies in childhood RMS can be tailored to patients' presenting characteristics. Bone marrow aspirate and biopsy and bone scan are unnecessary in at least one third of patients with RMS.