Optimal Timing to Surgery after Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer

Neoadjuvant chemoradiotherapy (nCRT) has demonstrated proven benefit in tumor regression and improved long-term local control for patients with locally advanced rectal cancer. However, precise analysis of the optimal waiting time that maximizes oncologic benefits of nCRT has not been established.

The 2006-2012 National Cancer Data Base was queried for patients with stage II and III rectal adenocarcinoma who underwent nCRT followed by surgical resection. Time to surgery was defined as the difference between last date of radiotherapy and date of surgery. Primary study endpoints included resection margin positivity and pathologic downstaging. Multivariable regression modeling with restricted cubic splines was used to evaluate the adjusted association between time to surgery and our study endpoints, and to establish an optimal time threshold for surgery.

A total of 11,760 patients were included. Median time to surgery was 53 days (interquartile range [IQR] 43 to 63 days). After adjusting for patient demographic, clinical, tumor, and treatment characteristics, our model determined an inflection point at 56 days after end of radiotherapy associated with the highest likelihood of complete resection and pathologic downstaging. With adjustment, the risk of margin positivity was increased in those who underwent surgery after 56 days from end of radiotherapy (odds ratio [OR] 1.40, 95% CI 1.21 to 1.61, p < 0.001). The likelihood of downstaging was increasing up to 56 days after radiotherapy (≥56 days vs <56 days, OR 1.2, 95% CI 1.02 to 1.23, p = 0.01).

This study objectively determined the optimal time for surgery after completion of nCRT for rectal cancer based on completeness of resection and tumor downstaging. Eight weeks appears to be the critical threshold for optimal tumor response.