Neoadjuvant immunotherapy and chemoradiotherapy for mismatch repair proficient locally advanced rectal cancer: A systematic review and meta-analysis.

Background: To evaluate the efficacy and toxicity of combining neoadjuvant immune checkpoint inhibitors (ICIs) with chemoradiotherapy (CRT) for patients with mismatch repair-proficient (pMMR) locally advanced rectal cancer (LARC).

Methods: PubMed, Embase, Cochrane Library, and Medline databases were searched. Phase I-III clinical trials reporting pathologic complete response (pCR) or overall CR (pCR + clinical CR) rates for neoadjuvant ICIs plus CRT in pMMR LARC were included. Studies that only enrolled patients with mismatch repair-deficient LARC were excluded. Data were analyzed at trial and arm levels and pooled using random-effects models. Primary outcomes were pCR and overall CR rates. Toxicity occurrence was also measured.

Results: In total, 19 trials (n = 1324) were included. At trial level, pooled odds ratios (95 % CIs) of overall CR and pCR rates for neoadjuvant ICIs plus CRT were 1.72 (1.21-2.44) and 1.68 (1.08-2.62), respectively. At arm level, compared with CRT, neoadjuvant ICIs plus CRT significantly improved overall CR (42 % vs 24 %, P < 0.001) and pCR rates (37 % vs 24 %, P = 0.008). Compared with ICIs plus long-course CRT, chemoimmunotherapy plus short-course radiotherapy significantly increased overall CR (51 % vs 36 %) and pCR (48 % vs 30 %) rates (both P < 0.001). Pooled incidence of grade 1-2 and ≥ 3 treatment-related adverse events was 63 % and 28 %, respectively-similar to CRT alone.

Conclusion: Neoadjuvant immunotherapy plus CRT is a promising treatment strategy for pMMR LARC, with improved CR rates and manageable toxicity. Chemoimmunotherapy plus short-course radiotherapy exhibits superior efficacy. Further investigation on long-term outcomes and optimal combined regimens is warranted.