Post-induction MRI response is associated with complete response and recurrence-free survival in rectal cancer treated with total neoadjuvant therapy.

OBJECTIVE: To evaluate the association between post-induction MRI response after induction chemotherapy and final treatment response in locally advanced rectal cancer (LARC) patients undergoing total neoadjuvant therapy. METHODS: This retrospective study included LARC patients who underwent induction chemotherapy-based total neoadjuvant therapy followed by total mesorectal excision (TME). MRI tumor regression grade and tumor longitudinal length reduction rate (TLLR) were used to assess post-induction response. MRI tumor regression grade and diffusion-weighted imaging were used to determine preoperative MRI complete response (mriCR). The primary outcome was the pathological complete response (pCR). RESULTS: The current study included 224 patients (56 [IQR 49-65] years). Good responders at post-induction evaluation were associated with higher mriCR (OR 3.78, p < 0.001), higher pCR (OR 4.41, p < 0.001), and better recurrence-free survival (p < 0.001). CONCLUSION: Post-induction evaluation was associated with later mriCR, pCR, and recurrence-free survival in LARC patients undergoing total neoadjuvant therapy, supporting future study on response-adapted neoadjuvant strategies.