A study by the University of Cambridge in the UK and the United States has revealed that breast cancer risk increases with age, with the most dramatic changes occurring at menopause. The researchers created the most detailed map of breast tissue changes to date, tracking over 3 million cells and uncovering a significant shift around menopausal women. The study found that as women age, the number of cells in breast tissue declines, and the structure of the tissue also changes, creating an environment where cancer cells thrive. This change explains why breast cancer risks increases due to a decrease in immune cells and stromal cells. Over 320,000 women in the US are expected to be diagnosed with breast cancer this year, making it the most common cancer in women.