Pelvic MRI Following Total Neoadjuvant Therapy for Rectal Cancer Poorly Predicts a Complete Clinical Response.

Area of Science:

• Oncology
• Radiology
• Surgical Oncology

Background:

• Assessing complete clinical response (cCR) after total neoadjuvant therapy (TNT) for rectal cancer is challenging.
• Discordant findings between endoscopy and pelvic MRI are common during post-treatment restaging.
• This study addresses discrepancies in restaging rectal cancer patients post-TNT.

Purpose of the Study:

• To evaluate outcomes for rectal cancer patients with endoscopic cCR but persistent radiographic disease on MRI after TNT.
• To compare outcomes between patients with and without residual disease on restaging MRI following nonoperative management (NOM).

Main Methods:

• Retrospective analysis of rectal cancer patients treated with TNT at UChicago (2015-2022).
• Inclusion criteria: endoscopic cCR, nonoperative management (NOM) pursued.
• Comparison of outcomes based on restaging MRI findings (residual vs. no residual disease).

Main Results:

• 30 patients achieved endoscopic cCR and pursued NOM.
• Restaging MRI revealed residual disease in 40% (12/30) and no residual disease in 60% (18/30).
• After a mean follow-up of 4.8 years, 30% (9/30) experienced tumor regrowth, with no significant difference between MRI groups (33% vs. 27.8%).
• 67% of patients with initially positive restaging MRIs showed no regrowth after 4 years.

Conclusions:

• A significant proportion of patients with endoscopic cCR and residual disease on MRI after TNT can safely undergo NOM.
• Initial positive restaging MRI findings in endoscopically negative patients did not predict regrowth.
• These results support NOM in selected rectal cancer patients even with discordant MRI findings post-TNT.