Abstract. Background Colorectal cancer (CRC) is one of the most common causes of cancer-related death worldwide (1). About 20-25% of patients with newly diagnosed CRC present with distant metastases (2-4), and only a small population of these patients can undergo curative operation (5). For patients with unresectable metastatic tumors, the standard treatment is systemic chemotherapy. As mentioned in the ESMO clinical practice guidelines (4), an individualized approach to clinical decision-making should be adopted according to the patient's stratification. Therefore, numerous attempts have been made to identify useful prognostic markers for accurate patient stratification.Anticancer immunity is known to affect cancer progression (6). Tumor-infiltrating lymphocytes (TILs), which reflect the immune status of the host (7), have been reported to correlate with the clinical outcome, including the chemotherapeutic outcome in patients with various types of cancer (8-10). However, the method of measuring TILs has differed among previous reports (11)(12)(13)(14)(15). Recently, a new method of measuring TILs in breast cancer was proposed by the International TILs Working Group, using H-E-stained sections (16). In the current study, we applied this method to CRC.The aim of the present study was to evaluate the significance of the TILs in the primary tumor as a marker for predicting the chemotherapeutic outcome in patients with stage IV CRC using the method proposed by the International TILs Working Group.
Patients and MethodsPatients. We retrospectively reviewed a database of 57 patients who underwent palliative combination chemotherapy for unresectable metastatic colorectal cancer after resection of the primary tumor at