A prospective evaluation of pelvic radiation vs. no radiation among patients with young-onset rectal cancer: Impact on patient-reported outcomes

3618 Background: The rise in young-onset rectal cancer (YORC) calls for better understanding of the long-term impact of radiation therapy(RT) on gastrointestinal(GI) toxicity and pelvic organ function. We aimed to prospectively capture the longitudinal trajectories of patient-reported outcomes(PROs) in YORC patients who received RT vs. no RT and to identify factors associated with unfavorable PROs. Methods: We prospectively enrolled 120 YORC patients undergoing curative-intent treatment. The validated EORTC QLQ-CR29 was self-administered at time intervals grouped as: 0-11 months, 12-23 months, and 24+ months post-resection. Responses were stratified by receipt of neoadjuvant RT (yes vs. no). The longitudinal change in PROs was described by a linear mixed effects model. Multivariate linear regression was used to determine the impact of treatment factors on long-term PROs. Results: The median age at diagnosis was 44. The majority (N = 92, 77%) presented with cT3,4/N+ disease. Preoperative therapy included: no RT (N = 38, 32%; 8 [7%] who received chemotherapy alone, and 30 [25%] who received no neoadjuvant therapy), vs. RT (N = 82, 68%; where 59 [72%] also received concurrent capecitabine). More patients in the RT group had advanced T stage (3 or 4; 94% vs. 56%, P< 0.001), distal tumor (median 7 vs. 12.5 cm from the anal verge, P< 0.01), and underwent abdominal perineal resection (19 vs. 0%, P< 0.001). After a median follow-up of 70 months, all were alive: 103 (86%) were disease-free, 9 (8%) had recurrence with successful salvage, and 8 (7%) had disease progression. In the RT group, sore skin improved at 12-23 and 24+ months (Estimate [ B]: -16.5, P= 0.03 and B: -14.4, P= 0.03), dyspareunia improved at 12-23 months ( B: -31.8, P< 0.01), and blood/mucus in stool improved at 24+ months ( B: -8.01, P< 0.01) vs. 0-11 months. At 24+ months, RT receipt was associated with worse stool frequency ( B: 26.4, P< 0.01), urinary frequency ( B: 18.4, P= 0.04), and flatulence ( B: 23.0, P= 0.02). Conclusions: YORC often require multimodality therapy including RT. Sore skin, dyspareunia, and blood/mucus in stool improved, but flatulence and frequency can persist beyond 2 years post RT. Proactive counseling and supportive measures are needed to inform treatment choices and mitigate long-term impact. [Table: see text]