The findings of this study build on earlier cancer research by Dr. Pollard and his team that shows macrophages can act at the primary tumor site to enhance tumor progression and malignancy. Thus, they've now shown that macrophages can become traitors, enhancing the worst aspect of the disease ??? metastatic tumor growth.

"This new study is important because it definitively shows the effects of macrophages at distant sites, as well as the identity of the macrophage population," Dr. Pollard explained. "This is the first proof that they have impact at this location, at the site of metastatic tumor growth."

Dr. Pollard noted that "metastatic disease is the major cause of cancer mortality," in part because the distant tumors tend to resist chemotherapy and radiation treatments. Unfortunately, "the biological mechanisms that underlie metastatic disease are poorly understood," so continuing research is needed. And if metastasis can somehow be blocked -- particularly through influencing cells of the metastatic microenvironment -- the impact on cancer mortality would be enormous.

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