Presence of S100A8/Gr1-Positive Myeloid-Derived Suppressor Cells in Primary Tumors and Visceral Organs Invaded by Breast Carcinoma Cells.

BACKGROUND: Increased S100A8/A9 expression in Gr1-positive cells has been shown in myeloid-derived suppressor cells and may play a role in the formation of a metastatic milieu. We aimed to determine S100A8/A9 expression alone and with coexpression of Gr1 (a myeloid marker) in primary tumor and visceral tissues invaded by metastatic breast carcinoma.

MATERIALS AND METHODS: Female BALB/c mice were injected with 4TLM, 4THM, and 67NR orthotopically. Confluent cells (75%-80%) were used. Primary tumor, lung, liver, and spleen tissue samples were removed 26 days after injection. Peripheral blood smears and metastasis assay were performed, as was immunohistochemistry and staining.

RESULTS: S100A8/A9 immunoreactivity alone or coexpressed with Gr1 was found in primary tumors formed by 4TLM and 4THM cells, which was markedly higher than in primary tumors formed by nonmetastatic 67NR cells. Similarly, liver and lung tissues obtained from mice injected with 4TLM or 4THM cells were invaded by S100A8/A9-positive and Gr1-positive cells. Double-positive cells were markedly fewer in liver and lung tissues of animals injected with 67NR cells. S100A8/A9-positive cells were mostly localized in red pulp of spleens. We observed an increased number of neutrophils in the peripheral blood of mice injected with metastatic breast carcinoma cells.

CONCLUSION: Tumor-derived factors may increase S100A8/A9-positive cells locally and systemically, and S100A8/A9-positive cells may provide an appropriate milieu for the formation of metastasis.