Objective To analyze the clinical characteristics of locally advanced rectal cancer patients with pathological complete response (pCR) after neoadjuvant chemoradiotherapy combined with immunotherapy.

Methods The retrospective cohort study was conducted. The clinicopatholo-gical data of 46 patients with locally advanced rectal cancer who were admitted to 6 medical centers, including Beijing Friendship Hospital of Capital Medical University et al, from June 2021 to November 2022 were collected. There were 29 males and 17 females, aged (61±4)years. Patients received neoadjuvant chemoradiotherapy combined with immune checkpoint inhibitor therapy, and under-went radical total mesorectal excision during 6-12 weeks after radiotherapy. Observation indicators: (1) comparison of clinical characteristics between pCR and non-pCR patients;(2) postoperative complications and adverse reactions of pCR and non-pCR patients. Comparison of measurement data with normal distribution between groups was conducted using the t test. Comparison of measurement data with skewed distribution between groups was conducted using the Mann-Whitney U test. Comparison of count data between groups was conducted using the chi-square test or Fisher exact probability. Comparison of ordinal data between groups was conducted using the Mann-Whitney U test.

Results (1) Comparison of clinical characteristics between pCR and non-pCR patients. Before neoadjuvant therapy, there were 14 cases aged ≥50 years and 6 cases aged <50 years in pCR patients, versus 25 cases and 1 case in non-pCR patients, showing a significant difference between the two groups (P<0.05). After neoadjuvant therapy, cases in clinical stage T0, T1, T2, T3, T4 were 11, 1, 5, 3, 0 for pCR patients versus 7, 4, 2, 11, 2 for non-pCR patients, cases of tumor regression grade 1, 2, 3, 4 were 11, 8, 1, 0 for pCR patients versus 7, 14, 4, 1 for non-pCR patients, cases in low-risk, medium-risk, high-risk of neoadjuvant rectal scoring and grading were 20, 0, 0 for pCR patients versus 4, 18, 4 for non-pCR patients, respectively, showing significant differences in above indicators between the two groups (Z=-2.256, -2.104, -5.458, P<0.05). (2) Postoperative complications and adverse reactions of pCR and non-pCR patients. Postoperative complications occurred in 2 cases of pCR patients and 5 cases of non-pCR patients, postoperative adverse reactions occurred in 11 cases of pCR patients and 10 cases of non-pCR patients, showing no significant difference between the two groups (P>0.05).

Conclusion Compared with locally advanced rectal cancer patients aged ≥50 years, those aged <50 years have significant benefits from neoadjuvant chemoradiotherapy combined with immunotherapy. Clinical T staging and magnetic resonance imaging-detected tumor regression grade after neoadjuvant therapy have predictive value for patients with pCR .