The role of restaging MRI post neoadjuvant therapy for locoregionally advanced rectal cancer

Background: Rectal cancer management has evolved from surgery to neoadjuvant radiotherapy to total chemoradiotherapy regimens. Magnetic resonance imaging (MRI) is the gold standard for staging; however, its role for assessing response to neoadjuvant therapy is less than clear. Objective: To assess the role of restaging MRI post neoadjuvant long-course chemoradiotherapy (NA CRT) for locoregionally advanced rectal cancer. Design: A retrospective audit of prospectively collected data. Setting: A tertiary hospital colorectal unit. Patients and Methods: Patients with locoregionally advanced rectal adenocarcinoma (T3/T4 and/or nodal disease), who underwent restaging pelvic MRI scans post-NA CRT were included. Medical records of relevant radiology and operative histopathology were reviewed. Main Outcome Measures: To determine whether restaging MRI altered subsequent patient management (compared to the initial plan as documented in the pretreatment colorectal multidisciplinary team meeting). Sample Size: Twenty-three patients with restaging MRI. Results: On diagnosis, 15 patients (65.2%) had American Joint Committee on Cancer (AJCC) stage-III disease; two patients had AJCC stage-II disease (8.7%), and five patients (21.7%) had AJCC stage-IV disease with limited metastases (curative intent to treatment). Three patients had a complete clinical response (cCR) post NA CRT. Fourteen tumors had downstaging (MRI tumor regression grade 2-3, 58.3%). In three patients (13.0%), restaging MRI altered patient management. Two of them had extensive disease that underwent significant downstaging, enabling avoidance of a pelvic exenteration; and one also had sufficient downstaging and was able to have a sphincter preserving operation as a result. Conclusions: MRI may have a role in patients with the extensive locoregional disease or in ultralow rectal cancers where it is unclear if sphincter preservation is possible. Limitations: Small sample size; additionally, "watch and wait" methods are not routinely practiced in this tertiary unit. Conflict of Interest: None.