Pathologic response and post-operative complications after short course radiation therapy and chemotherapy for patients with rectal adenocarcinoma

Abstract Background The role of neoadjuvant short course radiation therapy (SCRT) in treating rectal adenocarcinoma is a topic of ongoing debate. Growing interest in total neoadjuvant therapy has spurred discussion on the optimal sequence of preoperative SCRT and chemotherapy. Methods All patients receiving SCRT (5 Gray x 5 fractions) were identified. Details about preoperative treatments, radiation toxicities, and postoperative complications were collected. Patients were divided into two groups: those who underwent surgery within 14 days of completing SCRT and those with a longer delay. Outcomes compared included extent of pathologic response, margin-negative resection rate, acute radiation toxicities and postoperative complications. Results Fifty-seven patients with locally advanced or metastatic rectal cancer received SCRT between 2008 and 2018. Thirty-nine of fifty-seven patients underwent definitive pelvic surgery with total mesorectal excision (TME). There were no significant differences in tumor down-staging, radial margin status or percent tumor viability between patients with immediate surgery vs. delayed surgery. The delay group had higher rates of nodal down-staging (64.7% vs. 18.2%; p=0.003). There were no differences in total or grade 3+ gastrointestinal radiation toxicity, postoperative complications, reoperation, readmission, and mortality between the two groups. Conclusions Though not yet common in the U.S., SCRT has compared favorably to long course chemoradiation in multiple trials. Moreover, it is associated with greater efficiency and less disruption to chemotherapy. Our data show similar response and toxicity outcomes between the immediate and delay group, suggesting SCRT is well tolerated regardless of treatment sequence. Recently completed prospective trials may reveal the optimal preoperative treatment sequence.