A professor of human genetics at the David Geffen School of Medicine at UCLA, Steve Horvath, has found a way to measure tissue ageing which may explain why your risk of cancer increases as you age. He discovered this by measuring DNA methylation levels, which are epigenic changes to DNA. He found that in most cases, the chronological age of a tissue matched the biological age, by using information from normal and cancerous tissue and cells. Female breast tissue, about two or three years older than other tissues, was the only exception. This could reflect one of two things: the effect of hormones or the effect that cancer has on nearby healthy cells. Cancer has the ability to accelerate tissue ageing by a whopping average of 36 years. On average, the age of healthy cells near breast cancer cells are 12 years older than tissue in the rest of the body. This may explain why breast cancer is so common in women, and why cancer risk increases with age.