Obesity in women with triple-negative breast cancer, the most aggressive kind of breast cancer, reprograms immune cells and creates a chronic inflammatory environment that promotes cancer progression and spread, a study has found. The study, "Metabolically activated adipose tissue macrophages link obesity to triple-negative breast cancer," was published in the Journal of Experimental Medicine. Obesity is one of the major risk factors for the development of breast cancer, accounting for approximately 20% of all cancer-related deaths. Besides increasing overall breast cancer mortality, obesity also seems to increase a woman's chance of developing the most aggressive forms of breast cancer, including triple-negative breast cancer (TNBC). Previous studies have shown a strong relationship between obesity and disease progression among women with TNBC. However, the reasons why obesity predisposes these women to a poor prognosis are still unclear. Obesity has been shown to promote chronic inflammation in fat tissues by promoting the infiltration and activation of certain immune cells. Therefore, one hypothesis for the strong link between obesity and TNBC progression may be that these immune cells might be doing the same thing in mammary fat tissues, creating an inflammatory environment prone to tumor development.