Patterns of Failure in Parameningeal Alveolar Rhabdomyosarcoma

To determine patterns of failure, clinical outcomes, and prognostic factors among pediatric patients treated with radiation therapy for parameningeal alveolar rhabdomyosarcoma.

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.

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.

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.