Obese women are not only at a higher risk of breast cancer than their slimmer sisters — their cancer is more aggressive. Researchers at the University of Granada wanted to understand why.

They found that the type of fat that surrounds the tumor (peritumoral fat) helps the cancer stem cells (CSCs) to grow and invade surrounding tissues, making CSCs responsible for the onset and growth of the tumor.

CSCs are few in number, but they are responsible for cancer that spreads to parts of the body far from the original tumor (called metastasis). Conventional chemotherapy and radiotherapy treatments do not kill CSCs, and they are the reason that many patients suffer a relapse after appearing to respond well to a cancer treatment.