| Summary: | Abstract Background The anticancer immune response has been reported to correlate with cancer progression. Tumor-infiltrating lymphocytes (TILs), which are one of the indicators of host immunity, affect the tumor growth, metastasis and chemoresistance. Both TILs in the primary tumor and those in the metastatic tumor have been reported to be a useful predictor of the survival and therapeutic outcome. However, the correlation between the density of TILs in the primary and metastatic tumor is unclear. The aim of this study was to elucidate the correlation between the density of TILs in the primary and metastatic tumor. Methods A total of 24 patients with stage IV colorectal cancer who underwent concurrent resection of the primary tumor and liver metastasis were enrolled in order to assess the correlation between the density of TILs in the primary tumor and that in the metastatic tumor. Hematoxylin and eosin (HE)-stained tumor sections were used for the evaluation of TILs. The density of TILs was assessed by the measurement of the area occupied by mononuclear inflammatory cells over the total stromal area at the invasive margin. In addition, to evaluate TIL subsets and the activation/suppression status of the lymphocytes, immunohistochemistry for CD4, CD8, Forkhead boxprotein P3 (FOXP3), programmed cell death 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA4), inducible T-cell co-stimulator (ICOS), Glucocorticoid induced tumor necrosis factor receptor related protein (GITR), Human Leukocyte Antigen - antigen D Related (HLA-DR) and Granzyme B was performed, and the number of immunoreactive lymphocytes was counted. Results According to the evaluation using the HE-stained sections, the density of tumor-infiltrating mononuclear inflammatory cells in the primary tumor was significantly associated with that in the metastatic tumor. In addition, according to the immunohistochemistry evaluation, the density of CD4+, CD8+ and FOXP3+ TILs in the primary tumor and that in the metastatic tumor were significantly correlated with that in the metastatic tumor. Furthermore, the activation/suppression marker values of the lymphocytes (i.e., such as PD-1, ICOS, Granzyme B and the PD-1/CD8 ratio) in the primary tumor were correlated with values in the metastatic tumor. Conclusions The local immune status of the primary tumor was revealed to be similar to that of the metastatic tumor. This suggests that the evaluation of the local immunity of the primary tumor may be a substitute for the evaluation of the local immunity of the metastatic lesion. Therefore, information on the primary tumor may be useful when considering treatment strategies for metastatic lesions.
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