Tumor-infiltrating Lymphocytes Predict the Chemotherapeutic Outcomes in Patients with Stage IV Colorectal Cancer

Background/Aim: The anticancer immune response has been reported to contribute to the success of chemotherapy. The aim of this study was to evaluate the significance of the measurement of tumor-infiltrating lymphocytes (TILs) in the primary tumor using the method proposed by the International TILs Working Group as a prognostic marker of chemotherapeutic outcomes in patients with stage IV colorectal cancer (CRC). Patients and Methods: A total of 57 patients with stage IV CRC who underwent palliative chemotherapy after resection of the primary tumor were enrolled. Hematoxylin and eosin (H-E)-stained tumor sections were used for the evaluation of TILs. The density of TILs was assessed by measuring the area occupied by mononuclear inflammatory cells over the total stromal area at the invasive margin. Immunohistochemistry for CD8 was also performed, and the number of immunoreactive cytotoxic T-lymphocytes (CTLs) at the invasive margin was counted. Results: Thirty patients were classified into the high-TILs group, and 27 patients were classified into the low-TILs group. The high-TILs group had a significantly higher chemotherapeutic response rate (79.3% vs. 48.1%, p=0.025) and better progression-free survival (median survival time: 10.1 m vs. 7.3 m, p=0.0133) than the low-TILs group. Furthermore, the high-TILs group had a significantly better overall survival than the low-TILs group (median survival time: 35.5 m vs. 22.4 m, p=0.0221). The density of TILs evaluated using the H-E-stained sections showed a strong association with the number of CTLs (p<0.001). Conclusion: The measurement of TILs in the primary tumor using the method proposed by the International TILs Working Group can be used as a prognostic marker of the clinical effectiveness of palliative chemotherapy in patients with stage IV CRC.