The Role of Whole Abdomen and Pelvis Radiation Therapy in Desmoplastic Small Round Cell Tumor

Abstract

Desmoplastic small round cell tumor (DSRCT) is a rare entity that typically presents in adolescent and young adult men with widespread abdominopelvic disease. The benefit of whole abdomen and pelvis radiation therapy (WAPRT) after chemotherapy and maximal surgical resection is unknown. Our objective was to evaluate the oncologic benefit and toxicity of WAPRT in this rare and aggressive disease. We conducteda retrospective review of patients with DSRCT treated at our institution primarily between 2018-2021. The cumulative incidence (CI) of intra-abdominopelvic failure was compared among those who received WAPRT after chemotherapy and surgery vs those who received chemotherapy and surgery alone without WAPRT utilizing Gray's method. Progression-free survival (PFS) and overall survival (OS) were also compared among patients who did and did not receive WAPRT using the Kaplan-Meier method from the date of surgery. Toxicity was graded per CTCAE v5.0 criteria. Twenty-eight patients were included (median age 17.5 years; range 6-38 years; 78% male, 22% female). All patients received chemotherapy with VDC/IE, all but one underwent extensive tumor resection, and all but two received HIPEC at time of resection. Nineteen patients (median age 13 years) received WAPRT after surgery, while 9 patients (median age 24 years) were treated with systemic therapy and surgery alone. Patients who received WAPRT were generally treated to 30 Gy in 20 fractions utilizing intensity-modulated radiation therapy (IMRT), with a boost to gross disease to a total dose of 45-50 Gy in 9 patients. Median follow up was 20 months. The CI of intra-abdominopelvic failure at 12 and 24 months was 16% and 50% with WAPRT vs 74% and 87% without WAPRT (p = 0.003), with a median time from surgery to intra-abdominopelvic failure of 15 months after WAPRT vs 5 months without. PFS was also improved with WAP-RT (94% and 83% at 12 and 24 months) vs without WAPRT (67% and 0% at 12 and 24 months), p = 0.001. Among those who received WAPRT, patients who received a boost to gross disease had similar intra-abdominopelvic control as those who had no gross disease to boost and received WAPRT only (CI at 24 months 50% without boost vs 48% with, p = 0.95). OS did not differ between those who did and did not receive WAPRT (OS at 24 months, 88% vs 83%, p = 0.89). Most toxicities after WAPRT were mild, including grade 1-2 fatigue, nausea, and vomiting, with the exception of one patient who developed veno-occlusive disease. Although limited by selection bias and short follow up, our study shows durable intra-abdominopelvic control and an improvement in PFS after WAPRT with IMRT, without an effect on OS. Additional larger, prospective investigations evaluating the value and toxicity of WAPRT for DSRCT are warranted.