Potentials for endoscopic and magnetic resonance diagnostic methods in assessing the radicality of chemoradiotherapy in patients with rectal cancer

Background. One of the treatment options for patients with a histologically verified diagnosis of rectal cancer (RC) after chemoradiotherapy (CRT) at the first stage with a complete clinical response is an organ-preserving method consisting in follow-up. Given the possible risks of choosing this observation method, including continued tumor growth, high accuracy in assessing the response to CRT is required. The response of the rectum to CRT is assessed based on the results of a set of physical and instrumental diagnostic methods, including digital rectal examination, rectoscopy, and magnetic resonance imaging (MRI).

Objective. Comparison of the accuracy of the endoscopic examination method, supplemented by mandatory biopsy material collection, and MRI in assessing the complete clinical response after CRT.

Methods. In the period from 2017 to 2023, 117 patients with verified cancer of the middle and lower ampullar parts of the rectum were examined and treated at the N.N. Trapeznikov Research Institute of Cancer Research, N.N. Blokhin National Medical Research Center of Oncology. All patients underwent neoadjuvant CRT at the first stage of complex therapy.

Results. The effectiveness of the therapy was assessed based on the results of a clinical examination, including MRI and colonoscopy with biopsy. The reference standard for assessing the accuracy of the examination results was the conclusion of a histological examination based on the material taken during colonoscopy from the site of a previously localized tumor.

Conclusion. Clinical assessment of the performed CRT using a combination of MRI and endoscopy (+ biopsy) is the most accurate and effective strategy for identifying patients with a residual tumor or patients with a likelihood of continued growth, especially in some cases where it is possible to delay surgical treatment and maintain the patient’s functional status. The addition of MRI (including DWI) to an endoscopic examination improves diagnostic indicators and their combination can be recommended as a diagnostic algorithm after CRT.