Whole Abdominal Radiotherapy Is Tolerable and Effective in Children and Young Adults With Intra-Abdominal Sarcoma: A Canadian Sarcoma Research and Clinical Collaboration (CanSaRCC) Study.

Background: Whole abdominal radiotherapy (WART) is utilized in children, adolescents, and young adults with intra-abdominal sarcoma, but efficacy and toxicity are uncertain.

Methods: Sarcoma patients diagnosed at ≤39 years of age between 1998 and 2023 who received WART were identified from a national registry. Patient and tumor characteristics, treatment, response, and survival outcomes were assessed.

Results: Twenty patients with desmoplastic small round cell tumor (DSRCT) (n = 7), rhabdomyosarcoma (RMS) (n = 6), Ewing sarcoma, rhabdoid tumor, endometrial stromal tumor (each n = 1), and sarcoma not-otherwise-specified (NOS) (n = 4) were included. Among 17 patients who received WART as part of upfront therapy, 16 had abdominal metastatic disease (94.1%) (peritoneal deposits n = 9, malignant ascites n = 8 [including two with both peritoneal deposits and malignant ascites] and liver metastases n = 1), while one was initially localized. Median WART dose was 22.5 Gy (range: 10.5-30); median kidney and liver doses were 14.9 Gy (range: 7.7-20.7) and 21.0 Gy (range: 13.1-27.7), respectively. Three patients developed Grade 3 acute toxicity; diarrhea (n = 2) or elevated creatinine (n = 1); two RMS patients developed second malignancies. Two-year overall and progression-free survival estimates were 100% and 80% (95% confidence interval [CI]: 51.6%-100%) in RMS; 62.5% (95% CI: 32%-100%) and 50% (95% CI: 22.5%-100%) in DSRCT. Five-year cumulative incidence of abdominal recurrence was 33.3% (95% CI: 11.4%-57.3%) with WART failure in DSRCT (n = 2) and sarcoma NOS (n = 1). Three patients received WART following relapse; all recurred; two within the WART field.

Conclusions: WART is well tolerated among young sarcoma patients and provides meaningful local disease control when utilized in front-line adjuvant therapy.