Purpose: This research explored the association between CD163-labeled M2-type macrophages and cancer-associated fibroblasts (CAFs) in the tumor microenvironment (TME) of 38 colorectal cancer (CRC) liver metastases. In addition, we investigated the correlation differences between M2-type macrophages and CAFs in the tumor microenvironments of 38 primary colorectal cancer patients with confirmed liver metastases and 946 colorectal cancer patients, as well as possible mechanisms of action between the two cells.
Methods: The Immunohistochemistry (IHC) method was applied to detect the expression levels of M2-type macrophages and CAFs in the tissues of 984 cases of CRC and to analyze the correlation between M2-type macrophages and CAFs in colorectal cancer tissues. The IHC method was also applied to detect the expression levels of M2-type macrophages and CAFs in the liver metastases of 38 cases of CRC in the experimental group and to analyze the correlation between the two cells in liver metastases.
Results: 1. M2-type macrophages and CAFs expression were significantly higher in 38 primary colorectal cancer patients compared to 946 controls, and the expression of M2-type macrophages was significantly positively correlated with CAFs. 2. In 984 CRC cases, M2-type macrophages and CAFs expression levels were significantly higher in the cancer tissues than in the paired paracancerous tissues. 3. The expression levels of M2-type macrophages and CAFs in primary colorectal cancer were significantly higher in the experimental group than in colorectal cancer tissues without distant metastasis.
Conclusion: M2-type macrophages and CAFs are involved in the development of the colorectal cancer tumor microenvironment, and their interaction influences the initiation and progression of liver metastasis in colorectal cancer. It may provide new clinical ideas for early diagnosis of CRC liver metastases and searching for immune targets.

Keywords: M2-type macrophages, cancer-associated fibroblasts, colorectal cancer, liver metastasis