Objective To investigate the clinical value of magnetic resonance imaging (MRI) in predicting pathological complete response (pCR) after immunotherapy combined with neo-adjuvant therapy for local advanced rectal cancer.

Methods The retrospective and descriptive study was conducted. The clinicopathological data of 48 patients with local advanced rectal cancer who were admitted to Beijing Friendship Hospital of Capital Medical University from January 2020 to March 2022 were collected. There were 35 males and 13 females, aged 62(32‒77)years. Of 48 patients, 30 patients received neoadjuvant therapy, 18 patients received immunotherapy combined with neoadjuvant therapy. All patients underwent total mesorectal excision. Observation indicators: (1) T staging on MRI and postoperative pathological examination after neoadjuvant therapy and immunotherapy combined with neoadjuvant therapy; (2) changes of apparent diffusion coefficients (ADC) in pCR and non-pCR patients after neoadjuvant therapy and immunotherapy combined with neoadjuvant therapy; (3) evaluation of predictive performance of MRI for pCR after immunotherapy combined with neoadjuvant therapy. Measurement data with normal distribution were represented as Mean±SD, and t test was used for comparison between groups. Measurement data with skewed distribution were represented as M(range). Count data were expressed as absolute numbers or percentages. Sensitivity, specificity and accuracy were used to evaluate the predictive performance.

Results (1) T staging on MRI and postoperative pathological examination after neoadjuvant therapy and immunotherapy combined with neoadjuvant therapy. Of the 30 patients receiving neoadjuvant therapy, 1 patient in stage T2 showed stage T2 on both MRI and postoperative pathological examination after neoadjuvant therapy, 16 patients in stage T3 showed stage T0, T1, T2, T3, T4 of 0, 1, 6, 9, 0 cases and 3, 0, 8, 4, 1 cases on MRI and postoperative pathological examination respectively after neoadjuvant therapy, 13 patients in stage T4 showed stage T0, T1, T2, T3, T4 of 0, 0, 1, 2, 10 cases and 1, 0, 4, 7, 1 cases on MRI and postoperative pathological examination respectively after neoadjuvant therapy. The pCR rate was 13.3%(4/30) and the accuracy rate of MRI was 43.33% for patients with neoadjuvant therapy. Of the 18 patients receiving immunotherapy combined with neoadjuvant therapy, 12 patients in stage T3 showed stage T0, T1, T2, T3, T4 in 4, 2, 2, 4,0 cases and 5, 1, 1, 5, 0 cases on MRI and postoperative pathological examination respectively after immunotherapy combined with neoadjuvant therapy, 6 patients in stage T4 showed stage T0, T1, T2, T3, T4 in 0, 0, 1, 3, 2 cases and 4, 0, 0, 2, 0 cases on MRI and postoperative pathological examination respectively after immunotherapy combined with neoadjuvant therapy. The pCR rate was 50.0%(9/18) and the accuracy rate of MRI was 38.89% for patients with neoadjuvant therapy. (2) Changes of ADC in pCR and non-pCR patients after neoadjuvant therapy and immunotherapy combined with neoadjuvant chemoradiotherapy. Of the 30 patients receiving neoadjuvant therapy, the ADC differences were 0.30±0.04 and 0.21±0.17 for 4 pCR and 26 non-pCR patients, respectively, showing a significant difference (t=2.36, P<0.05). Of the 18 patients receiving immunotherapy combined with neoadjuvant therapy, the ADC change rates and ADC differences were 40%±14% and 0.39±0.14 for 9 pCR patients, versus 22%±13% and 0.21±0.12 of 9 non-pCR patients, showing significant differences in the above indicators (t=2.86, 2.79, P<0.05). Receiver operation charac-teristic curve analysis of ADC change rate and ADC difference associated with pCR for 18 patients receiving immunotherapy combined with neoadjuvant therapy suggested that the areas under the curve were 0.81 (95% confidence interval as 0.60‒1.00, P<0.05) and 0.86 (95% confidence interval as 0.70‒1.00, P<0.05), with cutoff values as 0.23 and 0.36, respectively. (3) Evaluation of predictive performance of MRI for pCR after immunotherapy combined with neoadjuvant therapy. For the 18 patients receiving immunotherapy combined with neoadjuvant therapy, the sensitivity, specificity, accuracy were 33.33%, 88.89%, 61.11% of stage T0 on MRI for predicting pCR, 88.89%, 55.56%, 72.22% of down-staging of T staging on MRI for predicting pCR, and all 77.78% of ADC difference greater than the cutoff value for predicting pCR.

Conclusions Patients with local advanced rectal cancer who received immunotherapy combined with neoadjuvant therapy achieve a higher pCR rate. ADC difference and down-staging of T staging on MRI can predict pCR effectively.