BACKGROUND: Adjuvant therapy after rectal cancer surgery is indicated in T4N0 or any T and nodal metastasis and/or risk factors for recurrences. The surrounding healthy tissue may be involved in terms of the cancerization field and immunosurveillance mechanisms and it is the one directly involved in adjuvant therapy, but it has never been investigated as a predictor of response. This study aimed to identify immune markers in the healthy mucosa surrounding rectal cancer that can predict pitfalls (recurrences and toxicity) of adjuvant therapy for locally advanced rectal cancer.
MATERIALS AND METHODS: This study is a sub-analysis of data from the IMMUNOREACT 2 observational cohort study (NCT04917263). This multicentric study collected healthy mucosa samples surrounding the neoplasms of patients with locally advanced rectal cancer. A panel of immune markers was retrospectively investigated at immunohistochemistry: CD3, CD4, CD8, CD8beta, Tbet, FoxP3, PD-L1, MSH6, and PMS2 and CD80. A prospective analysis was performed with flow cytometry to determine the proportion of epithelial cells expressing CD80, CD86, CD40, HLA ABC, or HLA DR and the proportion of activated CD8+ T cells, CD4+ Th1 cells, and T reg. Survival analysis and ROC curve analysis were performed to assess the accuracy of immunological markers in healthy rectal mucosa in predicting recurrence and toxicity.
RESULTS: A total of 210 patients from the retrospective cohort were analyzed with immunohistochemistry, while 107 ones from the prospective cohort were analyzed using flow cytometry. In the retrospective cohort, a low level of CD4+ T-cell infiltration was a predictor of local recurrence (AUC=0.83 (95% CI 0,71 to 0,90, p<0.001) while a high level of Tbet+ cell infiltration was a predictor of liver recurrence (AUC=0.74 (95% CI 0,62 to 0,849, p=0.03). Moreover, in the retrospective cohort of patients, CD8+ T cell infiltration was a good predictor of G3-G4 toxicity at adjuvant therapy (AUC=0.73 (95% CI 0,596 to 0,839, p=0.043). In the prospective cohort, low CD3+CTLA4+ cells rate (HR=6,8; 95% CI=1,16 to 40,53 p=0,03) and adjuvant therapy (HR=0,14; 95% CI=0,028 to 0,686 p=0,016;) were both independent prognostic factors of good overall survival.
CONCLUSIONS: Our findings suggest that low CD4+ T-cell infiltration in the healthy rectal mucosa may be a good predictor of local recurrence despite adjuvant therapy while a high level of Tbet+ cell infiltration may be a predictor of liver recurrence. Moreover, CD8+ T-cell infiltration resulted to be a good predictor of toxicity at adjuvant therapy. Thus, these easily performed immunohistochemical tests might be used in the decision-making in patients with rectal cancer candidates for adjuvant therapy. Finally, a low CD3+CTLA4+ cell rate is associated with good overall survival supporting the potential role of immunotherapy in rectal cancer management.

Giulia Casale

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