Infantile myofibromatosis: Excellent prognosis but also rare fatal progressive disease. Treatment results of five Cooperative Weichteilsarkom Studiengruppe (CWS) trials and one registry

Background Infantile myofibromatosis (IM) is a rare benign soft tissue tumor and often a self-limiting disease but rarely includes life-threatening complications. Little is known about optimal treatment of primary localized (LD) and multifocal disease (MFD). Methods Treatment and outcome of 95 children with IM registered within five Cooperative Weichteilsarkom Studiengruppe (CWS) trials and one registry (1981-2016) were evaluated. Results LD was diagnosed in 71 patients at a median age of 0.4 years (range 0.0-17.7). MFD was present in 24 patients. The mainstay of treatment was watch-and-wait strategy (w&w) after initial biopsy or resection. Low-dose chemotherapy (CHT) was administered to 16/71 (23%) patients with LD and eight of 24 (33%) patients with MFD, imatinib was added in two. A delayed resection was possible in eight of 71 (11%) and five of 24 (21%) patients with LD and MFD, respectively. Overall, patients were alive in complete remission (n = 77) and partial remission (n = 10) at a median follow-up time of 3.4 years after diagnosis (range 0.01-19.4); no data available (n = 5). Three patients died of progressive disease (PD) despite CHT. Gender, tumor size, and location correlated with a favorable event-free survival (EFS) in patients with LD. The 5-year EFS and overall survival of patients with LD were 73% (+/- 12, confidence interval [CI] 95%) and 95% (+/- 6, CI 95%), respectively; for MFD 51% (+/- 22, CI 95%) and 95% (+/- 10, CI 95%). Conclusion Prognosis is excellent in patients with LD and MFD. Targeted treatment needs to be evaluated for rare fatal PD.