Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma

Purpose: To determine patterns of failure, clinical outcomes, and prognostic factors among pediatric patients treated with radiation therapy for parameningeal alveolar rhabdomyosarcoma. Methods and Materials: We evaluated clinical and treatment planning records of patients aged ≤21 years with parameningeal alveolar rhabdomyosarcoma treated with definitive or adjuvant radiation therapy at our institution. The Kaplan-Meier product limit method assessed disease control and survival; the log-rank test was used to evaluate prognostic impact. Results: We identified 24 patients with a median age of 3.5 years (range, 1-20) treated between 2009 and 2016. The median follow-up was 2.4 years for all (range, 0.3-5.6) and 3.2 years for living patients (range, 0.7-5.6). Most patients had group III (96%), node-negative (67%), positive FOX fusion status (63%) disease, and intracranial extension (54%). The paranasal sinus was the most common subsite (29%). All patients were treated with concurrent chemotherapy and proton radiation therapy with a median dose of 50.4 Gy relative biological effectiveness (range, 41.4-59.4) at a median 13 weeks after induction chemotherapy (range, 3-25). The 3-year local control, regional control, disease-free survival, and overall survival rates were 66%, 94%, 40%, and 58%, respectively. Median time to any failure was 0.5 years (range, 0.2-2.1). N1 disease and intracranial extension (ICE) portended inferior overall survival (P = .002 and .02, respectively). Female sex portended better local control (P = .05). All 7 patients with distant metastases as the first site of recurrence had central nervous system metastases. Age <4 years, absence of ICE, N0 disease, and primary tumor <5 cm were associated with a statistically significant improvement in freedom from distant metastases. Conclusions: Although regional nodal failures were rare, in-field local recurrences and leptomeiningeal progression in those with ICE suggest the need for modification of local and central nervous system therapies.