Women who are genetically predisposed to breast cancer often have a family history of the disease, although little is known about the factors that actually initiate tumour development. Now, an epidemiological study of female twins — published in The New England Journal of Medicine (5 June 2003) — indicates that puberty might trigger breast cancer in women who are genetically susceptible to this disease.

Ann S. Hamilton and her co-author Thomas M. Mack examined 1,811 pairs of twins — one or both of whom had breast cancer — and looked for associations with age at puberty, menopause and pregnancy. If both twins had breast cancer — assumed to be the hereditary form — they found that the first twin to reach puberty was five times more likely to have developed breast cancer earlier. But for twins with non-hereditary breast cancer — affecting only one twin — the age of puberty onset did not affect risk. So, Hamilton proposes that “...within the general population, there exists a subset of women who may be at increased risk of developing breast cancer from exposure to hormones at the time of puberty” (Reuters Health, 5 June 2003).

According to Hamilton, “ We still have a lot to learn about breast cancer and the genetic factors that have been identified so far do not account for all the cases of breast cancer thought to be associated with genetic susceptibility” (Reuters Health). “This [study] provides some more clues about a different approach in looking for genetic factors” (New York Times, 5 June 2003).