Background

Tumor-associated macrophages (TAM) plastically change their polarity to M2macrophages (M2Mϕ) in the tumor microenvironment. It has been reported correlation of tumor-infiltrating TAM with lymphangiogenesis and lymph node (LN) metastasis of several types of cancer including gastric cancer (GC). However, It is not sufficiently elucidated that the role of intranodal TAM on tumor progression of GC. The purpose of this study was to examine the distribution of intranodal TAM in draining LNs and the association of M2Mϕ with spreading LN metastasis of GC.

Methods

We assessed regional LN specimens from 49 patients with GC who are composed of pathologically diagnosed 31 node-positive and 18 node-negative cases. All specimens were examined by immunohistochemistry staining of cytokeratin AE1/AE3 antibodies for tumor cells and CD163 antibodies for M2Mϕ. The distributions of intranodal macrophages were analyzed by calculating the number of M2Mϕ according to the region of the cancer location. PBMC harvested from blood samples of healthy subjects were ascertained to be differentiated into M1, M2a and M2cMϕ by appropriate cytokines. Vascular endothelial growth factor-C (VEGF-C) concentrations of Mϕ supernatants were detected to compare the ability of lymphangiogenesis.

Results

The number of M2Mϕ infiltrating in the LNs with metastasis were significantly higher than that of normal LNs (p<0.0001). In the histopathological examination, stage and degree of LN metastasis positively correlated with the number of intranodal M2Mϕ. The number of intranodal M2Mϕ was decreased distant from the primary tumor. Importantly, M2Mϕ increased at LNs along root of the left gastric artery and gastroepiploic arteries in patients with node positive. The VEGF-C levels of the M2Mϕ culture supernatants were significantly higher than that of control Mϕ. The result of flow cytometer revealed that M2a and M2c cultured from PMBC expressed CD163.

Conclusion

The number of intranodal M2Mϕ significantly associated with LN metastasis and progression of GC. Moreover, M2Mϕ infiltrated into LNs prior to formation of metastasis. The findings indicated that M2Mϕ might migrate into LNs by chemotactic activity of primary tumor. Our results suggested that molecules associated with M2Mϕ could be one of the new biomarkers for LN metastasis of GC.

Citation Format: Yukie Go, Hiroaki Tanaka, Mao Tokumoto, Yoshihiro Okita, Masatsune Shibutani, Sadaaki Yamazoe, Katsunobu Sakurai, Hisashi Nagahara, Kenjiro Kimura, Takahiro Toyokawa, Ryosuke Amano, Naoshi Kubo, Kazuya Muguruma, Hiroshi Otani, Masakazu Yashiro, Kiyoshi Maeda, Masaichi Ohira, Kosei Hirakawa. Extent of intranodal macrophage correlates with lymph node metastasis of gastric cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1081. doi:10.1158/1538-7445.AM2014-1081