Birth size a marker for breast cancer later in life

A new study by researchers at the London School of Hygiene and Tropical Medicine has found that birth size is a marker of susceptibility to breast cancer later in life - they say birth size, and in particular birth length, is associated with an increased risk of breast cancer in adulthood.

The researchers say their analysis of 32 studies involving more than 600,000 women provides the strongest evidence yet of such a link and birth size might explain 5% of all breast cancers, suggesting some link between cancer and the environment of the baby before birth.

The new study, led by Professor of Epidemiology, Dr. Isabel dos Santos Silva, re-analysed the data from the studies to obtain more precise estimates of the extent to which birth size affects the risk of breast cancer later in life and to investigate whether they could be explained by associations with other risk factors.

There were 22,058 cases of breast cancer among the women, most of whom lived in developed countries and the research team found that birth weight was positively linked to breast cancer risk - a 0.5 kg increment in birth weight was associated with an estimated 7% increase in the risk of breast cancer.

Birth weight, length and head circumference were all linked with breast cancer risk possibly because a larger baby may be exposed to more oestrogen and other hormones in the womb, but birth length appeared to be the strongest independent predictor of risk.

The risk of developing breast cancer by the age of 80 was 11.5 in 100 for the women who measured more than 51cm (20in) in length at birth, compared with 10 in 100 for those who had measured less than 49cm (19.3in).

Experts say breast cancer is a complex disease that can be influenced by many factors throughout a woman's life and although there was nothing a woman could do about her size at birth, she could help reduce her risk of developing breast cancer by maintaining a healthy weight, eating a balanced diet and limiting her alcohol intake.

The researchers say the increase in risk, although modest, is of a similar magnitude to that of other more established risk factors for breast cancer, such as alcohol consumption.

Professor dos Santos Silva says little is known on how the pre-natal environment may affect breast cancer risk in later life and more research is needed - she says it is vital that all women remain breast aware throughout their lives and undergo regular routine breast screening.

The study is published in PLoS Medicine.