(P 165) MIDDLE EAR RHABDOMYOSARCOMA: A REPORT FROM THE CHILDREN'S ONCOLOGY GROUP

Objective: Middle ear rhabdomyosarcoma (ME RMS) is often locally advanced at diagnosis with extension occurring through the tympanic membrane, intracranially, or laterally in front of or under the ear, but rarely metastasizes distantly. Prior studies suggest ME RMS may have a more favorable outcome than other parameningeal sites. We describe the presentation and outcomes of patients with ME RMS treated on recent Children’s Oncology Group clinical trials.

Methods: Patients with ME RMS enrolled on Children’s Oncology Group Studies for newly diagnosed rhabdomyosarcoma from 1997 to 2013 were identified. Demographic information, tumor characteristics and survival information were analyzed using descriptive and survival statistics.

Results: Forty-four patients with ME RMS were identified. Twenty-seven (61.4%) were treated on D9803, 16 (36.4%) on ARST0531, and 1 (2.3%) on ARST0431. There were no patients with ME RMS treated on D9602, D9802, ARST0331, or ARST08P1. The majority (65.9%) were male, and between 1 to 9 years old (97.7%). Tumor histology was most commonly botryoid RMS (43.2%), followed by embryonal RMS (38.6%), with only 4.5% alveolar histology. The majority (77.3%) had tumors less than or equal to 5 cm in greatest diameter. Lymph node involvement was identified in 22.7%, and distant metastatic disease in only 4.5%. Most tumors were classified as stage 2 (59.1%) or stage 3 (36.4%), with the vast majority being IRS Group III (93.2%). Most patients (97.7%) received radiation therapy. The 4-year event free survival (EFS) for the whole cohort was 75%% (95% CI 61.8-88.2), and overall survival (OS) 79.3% (95% CI 66.1-92.0). There was no difference in EFS or OS related to tumor size. While there was no significant difference between outcomes related to trial of entry, it is notable that the 4 year EFS and OS on D9803 were 81.55% (95% CI 66.8-96.1 ) and 85.2% (95% CI 71.5-98.9) compared with 62.5% (95% CI 35.9-89.0) and 67.7% (95% CI 41.0-94.4) on ARST0531. The single patient enrolled on ARST 0431 was a long-term survivor.

Conclusion: While not statistically significant, we demonstrate a trend toward worse EFS and OS for patients treated on ARST 0531, which used a lower cumulative cyclophosphamide dose than study D9803. This is consistent with a prior report demonstrating a significantly higher local failure rate with lower dose cyclophosphamide for head and neck rhabdomyosarcoma and a trend toward worsened EFS. (PMID 30508617)