Scientists Discover Link Between Nicotine and Breast Cancer Metastasis

This environment is called a pre-metastatic niche, which attracts pro-tumor neutrophils, a type of immune cells. The pre-metastatic niche releases a protein called STAT3-activated lipocalin 2 (LCN2) from the neutrophils to induce metastatic growth.

For the study, Watabe's team first studied 1,077 breast cancer patients and found that current smokers or former smokers have a higher incidence of lung metastasis compared to patients who never smoked.

Then, using a mouse model of breast cancer metastasis, the researchers discovered that persistent exposure to nicotine generates an inflammatory microenvironment in the lungs characterized by an influx of activated neutrophils to create a pre-metastatic niche.

Even after quitting nicotine for 30 days, the incidence of distant metastasis was not reduced, suggesting an ongoing risk for breast cancer patients who are former smokers.

Watabe and colleagues also looked for a drug that might block this accumulation of neutrophils and identified salidroside, a natural compound found in the plant Rhodiola rosea. This compound, which has anti-inflammatory, anti-cancer and anti-viral properties, significantly decreased the number of pro-tumor neutrophils and subsequently reduced the incidence of lung metastases in mice.

"Based on these findings, breast cancer patients should opt for smoking cessation programs that do not use nicotine replacement products," Watabe said. "Furthermore, our findings show that salidroside may be a promising therapeutic drug to help prevent smoking-induced breast cancer lung metastasis, although more research is needed."