Optimal timing of surgical resection after radiation therapy in locally advanced rectal adenocarcinoma: An analysis of the National Cancer Database (NCDB).

510 Background: In treatment of rectal adenocarcinoma, an increased time delay (TD) of 6-12 weeks from the end of radiation therapy to surgery may increase the rate of complete pathologic response (pCR), but the optimal TD with respect to survival has not been established. This study evaluates the impact of TD on overall mortality. Methods: The NCDB was queried for patients with adenocarcinoma of the rectum and no evidence of metastasis at diagnosis, who underwent preoperative chemoradiation followed by radical surgical resection. Standard statistical methods were employed for descriptive statistics and Cox model development. Results: The study included 6805 patients, predominantly Caucasian (87.2%) and males (63.9%) who generally were treated with low anterior resection (57.3%), colonanal reanastomosis (8.4%), or abdominoperineal resection (28.4%), and had median survival of 66.6 months. The effects of age, surgical margins (-/+), comorbidity index, time to discharge after surgery, TMN pathologic staging, surgical volume, and patient income significantly impacted mortality after radiation and surgery (p<0.05 for all values). There was a significant relationship between TD and pCR (p=.0002). At TD less than 30 days, 4.0% of patients achieved pCR, while 9.3% of patients have achieved pCR by 75 days. In TD of greater than 75 days, the rate of pCR decreased. Overall, 6.8% of patients (n=461) achieved pCR. Using a refined cox model, a TD of more than 60 days was associated with 20% greater risk of mortality (95% CI 1.068 – 1.367). This effect became more pronounced with increasing TD; a TD of greater than 75 days was associated with 28% (95% CI 1.06-1.55) increased risk of mortality, while patients with TD less than 60 days saw a survival benefit. Conclusions: Though an interval up to 75 days between radiation and surgery may achieve higher rates of complete pathologic response, delay of more than 60 days from radiation to surgical resection and subsequent systemic chemotherapy decreases overall survival in patients with rectal cancer.