The significance of tumor-infiltrating lymphocytes before and after neoadjuvant therapy for rectal cancer

Summary

Recently, neoadjuvant therapy for locally advanced rectal cancer has been generally performed. However, biomarkers predicting the response to neoadjuvant therapy have not been established. Tumor-infiltrating lymphocytes (TILs) have a crucial effect on tumor progression and the survival outcome as the primary host immune response, and an antitumor immune effect has been reported to contribute to the response to radiotherapy and chemotherapy. We investigated the significance of TILs before and after neoadjuvant treatment and the change in the density of those TILs. A total of 64 patients who underwent radical resection after neoadjuvant treatment for locally advanced rectal cancer were enrolled. The number of TILs subsets was examined using immunohistochemical staining of pretreatment biopsy samples and posttreatment resected specimens. In both the neoadjuvant chemotherapy cohort and the neoadjuvant chemoradiotherapy cohort, a low density of CD8⁺ TILs in pretreatment biopsy samples was associated with a poor response, and a low density of CD8⁺ TILs in posttreatment resected specimens was similarly associated with a poor response. In the neoadjuvant chemoradiotherapy cohort the density of CD8⁺ TILs in posttreatment resected specimens was significantly increased compared with that in pretreatment biopsy samples. We concluded that T lymphocyte-mediated immune reactions play an important role in tumor response to neoadjuvant treatment for rectal cancer, and the evaluation of TILs in pretreatment biopsy samples may be a predictor of the clinical effectiveness of neoadjuvant treatment. Furthermore, neoadjuvant therapy, especially chemoradiotherapy, may induce the activation of the local immune status.

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