Oncological Short-term Effects and Adverse Events of MRI-guided Selective Neoadjuvant Radiochemotherapy for Rectal Cancer

Aim: To investigate the oncological short-term effects and acute side-effects of magnetic resonance imaging (MRI)-guided selective neoadjuvant radiochemotherapy (nRCT) for rectal cancer. Patients and Methods: In a prospective multicenter cohort study of 230 patients with rectal cancer stage II or III, nRCT was applied in the following situations (n=96) only: cT4 tumors, cT3 tumors of the distal rectum or tumors leaving a circumferential resection margin (CRM) of ≤1 mm between the tumor and the mesorectal fascia (mrCRM+). Pre-therapeutical tumor stage and involvement of mesorectal fascia were assessed by MRI and were compared with the pathological findings of the rectal specimens. Furthermore, tumor regression grades, acute side- effects, and surgical complications were analysed. Results: Using selective nRCT, 62 out of 72 patients (86%) with mrCRM+ had tumor-negative pathological CRM. Reduction of T category was observed in 62% and of N category in 88% of patients. Lymph node metastasis was found by pathology in only 21% of all irradiated patients. Histologically complete tumor regression (ypT0ypN0) was observed in 15% and intermediate regression (more than 25%, but not complete) in 67% of patients. Fifteen percent of patients suffered from grade 3 toxicity, but no grade 4 toxicity occurred. nRCT did not adversely influence surgical morbidity. Conclusion: Despite the negative selection of locally advanced rectal cancer cases for nRCT, impressive rates of tumor down- staging and eradication of tumor from the mesorectal fascia were achieved. The rate of complete regression is comparable to that in the literature. Moreover, the selective use of nRCT spared a considerable percentage of patients with stage II/III rectal cancer severe irradiation toxicity.