Immunotherapy In Locally Advanced Rectal Cancer

Preoperative CTRT is considered the standard of care in the management of LARC. Preoperative CTRT approach results in significant tumor downstaging and local control with a complete pathological response rate of about 15% even if additional therapeutic strategies should be explored to improve outcomes, expecially for T4 cancers. Immunotherapy with PD-1/PD-L1 immunocheckpoint blockade (ICB), turned out a breakthrough in cancer treatment among different tumor types, including CRC. An ICB strategy could lead up to a 40% of response in metastatic CRC with deficient mismatch repair (MMR) status. Unfortunately, the activity of ICBs in MMR proficient mCRC is extremely low but it might be improved using immunomodulatory strategies as demonstrated by Bendell et al. In this context, the role of RT in revert the tolerance to a low neoantigen-burden (such as in MMR proficient CRCs) by the induction of antigen release from the tumour and activation of dendritic cells leading to a CD8+ T lymphocyte-mediated anticancer immune response has been widely elucidated. Moreover, antineoplastic agents can be exploited to target other crucial cellular effectors of immunosuppressive tumor microenvironment (i.e. regulatory T cells and myeloid-derived suppressor cells). In line with these evidences, Hecht et al. have recently reported that in rectal cancer patients, neoadjuvant CTRT increases PD-L1 expression in tumor cells, strongly suggesting a neoadjuvant combinatory strategy with RT and PD-1/PD-L1 pathway blockade. The integration of immunotherapy in the neoadjuvant setting (instead of adjuvant one) for the management of LARC is also supported by preclinical findings showing that in metastatic breast cancer mice models, neoadjuvant immunotherapy is superior in inducing long-term survivors, compared with adjuvant strategy with a greater magnitude of tumor-specific T cell expansion in neoadjuvant treated mice and a better anti-tumor T cell-mediated immune response. On the basis of such