Callan, Alexandra K.

10032 Background: Identifying clinical and biological factors associated with outcomes in localized Ewing sarcoma (ES) will enable risk-stratified clinical trials with the goal of improved outcomes for high-risk patients and decreased treatment toxicity for low-risk patients. The specific aims of this analysis in localized ES patients were 1) to classify extraosseous (EO) primary tumors with subdivisions into deep (viscera, glands, body cavities, muscle, nerves) and superficial (cutaneous and subcutaneous) sites, and 2) to understand the relationship between baseline clinical factors (age, sex, primary tumor site, size (maximum dimension and volume)) and event-free survival (EFS). Methods: The analytic cohort included ES patients treated with ICC on AEWS0031 and AEWS1031. Primary tumor sites were defined as pelvic, non-pelvic, and EO (deep vs. superficial). Post-enrollment EFS was the primary endpoint. Univariate analyses used the Kaplan–Meier method (logrank test). Multivariable analyses used Cox proportional hazards models. To assess the impact of tumor volume as a continuous variable, a subgroup analysis was conducted using AEWS1031 only, as tumor volumes were collected prospectively on this study. Visual exploration of effects of continuous variables on EFS event hazard used restricted cubic splines with 3 knots. Tests were performed at the 5% level. Results: AEWS0031 (n = 628) and AEWS1031 Regimen B (n = 283) yielded 911 patients. In univariate analyses, difference in risk of EFS event was observed between tumor sites ( P = 0.03). EO tumors had the highest estimated EFS compared to pelvic and non-pelvic (5 year EFS 84.7% vs. 72.4% and 75.9%). Superficial EO appeared to be a very low-risk group, albeit interpretations are limited by the small group size and singular event (one second malignant neoplasm among 15 patients). In multivariable analysis of the combined cohort, sex, race, and ethnicity were not prognostic. EO tumors may be associated with decreased hazard compared with non-pelvic bone primaries (HR 0.58, P = 0.07), and tumors ≥200 mL with increased hazard (HR 1.56, P < 0.01). In the subgroup analysis, tumor volume and age were prognostic and in visualizations age was non-linearly related to the hazard of EFS event, increasing until approximately 15 years. Tumor volume was non-linearly related to the hazard of EFS event and increased until approximately 400 mL. Conclusions: Patients with ES and primary tumors ≥200 mL continue to be at higher risk of an EFS event when treated with ICC, and EO tumors may be lower risk compared with other sites. Risk of an event appears to remain constant in ES patients ≥15 years or with primary tumors ≥400 mL. These findings should be validated in prospective trials and tumor biology integrated with clinical factors to improve risk stratification for localized ES.

AbstractPatients with resectable Ewing sarcoma (ES) in select sites, such as the pelvis or chest wall, have a higher risk of positive microscopic margins following surgery. AEWS1031 was the first North American/Australasia ES cooperative group trial allowing standardized preoperative radiotherapy, intended to minimize the morbidity of combined modality local tumor control as well as improve the likelihood of clear surgical margins. In this study, we found that the use of low‐dose preoperative radiation to a smaller target volume resulted in a high rate of R0 resection. The robust pathologic response rate strengthens existing evidence illustrating the radiosensitivity of Ewing sarcoma.

Ewing sarcoma and osteosarcoma constitute 36% of all primary bone cancers. However, these 2 subtypes represent the most commonly diagnosed bone cancer types in the pediatric and adolescent population. Although still largely unknown, certain genetic mutations, rearrangements, and/or predisposition syndromes likely play a role in the pathogenesis of bone cancer. Osteosarcoma may also develop as a direct result of the long-term side effects of radiation therapy. With the implementation of a multimodality approach to treatment, including multiagent neoadjuvant and adjuvant chemotherapy regimens, targeted therapy options, surgery, and radiation, individuals with Ewing sarcoma and osteosarcoma are showing higher cure rates and improved overall survival. The NCCN Guidelines for Bone Cancer provide a consensus and evidence-based framework for the workup, management, and surveillance of local and recurrent/metastatic disease.

11529 Background: To evaluate clinical characteristics and patterns of treatment failure in patients with localized Ewing sarcoma (ES) treated on AEWS1031 according to local control (LC) strategies, tumor size, and tumor site. Methods: AEWS1031 was a phase 3 randomized trial comparing two interval compressed chemotherapy regimens. Patients who completed LC on AEWS1031 were analyzed. LC was with surgery alone (S), definitive radiation therapy (RT), or surgery plus radiation (S+RT), and determined by the treating investigator. Local failure (LF) and distant failure (DF) were defined as recurrence at primary tumor site or distant site, respectively. Fine and Gray method was used to estimate cumulative incidence of LF and DF from time LC was completed. P-values were calculated using logrank or Gray’s test, as appropriate. A two-sided p-value of ≤0.05 was considered significant. Results: 588 patients completed LC. Median age at enrollment was 13.0 years (range: 0.6- 33.9 years). Tumor sites were categorized as extremity (230; 39%), axial (142; 24%), extraosseous (110; 19%), and pelvis (106; 18%). At diagnosis, tumor volume (TV) was ≥200 mL in 170 patients (31%) and maximum tumor dimension (MTD) was ≥8 cm in 289 patients (52%). LC was with S in 320 patients (54%), RT in 160 (27%), and S+RT in 108 (18%). Eight patients received preoperative RT. Fifty-three patients (13.1%) who received S±RT had an R1 resection. LC with S was more likely for extremity (58%), RT for pelvis (38%) and S+ RT for axial (36%) and extraosseous (34%) primary tumors (p <0.01). With median follow up of 67.6 months from LC, the 5-year cumulative incidences of LF and DF for the entire cohort were 6.0% (95% CI, 4.3-8.3%) and 11.0% (95% CI, 8.6-13.9%), respectively. Eleven patients experienced simultaneous LF and DF. LF incidence was 5.0% for S, 8.4% for RT, and 5.6% for S+RT (p=0.47). DF incidence was 11.8% for S, 6.4% for RT, and 15.1% for S+RT (p=0.16). LF incidence by tumor site was 3.6% for extremity, 8.7% for pelvis, 7.3% for axial, and 6.8% for extraosseous (p=0.08). LF incidence was higher for primary tumors ≥200 mL (11.3%) compared to tumors < 200 mL (3.9%; p<0.01) and for tumors ≥8 cm (7.8%) compared to tumors < 8 cm (4.4%; p=0.02). Tumor size was associated with a higher LF incidence for S and RT, but not for S+RT (Table). LF incidence was 4.0% for R0, 7.5% for R1 with RT, and 16.7% for R1 without RT (p=0.02). Conclusions: We report the lowest LF incidence to date for prospective ES trials conducted. Both larger TV and MTD were associated with higher LF. Future investigations will aim to evaluate the impact of chemotherapy dose-intensity on LC and identify risk-stratification variables for improved LC. Five-year LF incidence by LC and tumor size. Clinical trial information: NCT01231906 . [Table: see text]