STUDY: Link between birth size and breast cancer

JOURNAL: BMJ 2003;326:248-251.

AUTHORS: Dr. Valerie McCormack

ABSTRACT: Birth size, as determined by birth length and head circumference, is directly related to the risk of developing premenopausal breast cancer.

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COMMENTARY: However, the link between birth size and breast cancer was not seen among women older than 50 years of age, lead author Dr. Valerie McCormack, from the London School of Hygiene and Tropical Medicine, told Reuters Health.

Dr. McCormack said that the current study, reported in the February 1st issue of the British Medical Journal, was undertaken to investigate how conditions in the womb, which can influence birth size, might also influence the risk of breast cancer later in life.

Based on the findings, Dr. McCormack suggested that larger infants may have been exposed to different levels of growth hormones in the womb, and that the in utero environment may have played a role in determining breast cancer risk.

In the study, the researchers reviewed information from 5358 singleton females born between 1915 and 1929. Data from the Swedish Cancer Registry were analyzed to determine which subjects developed breast cancer.

The researchers found that 359 of the subjects developed breast cancer, with a median age at diagnosis of 62 years.

Women who weighed at least 4000 g at birth were 3.5 times more likely to develop breast cancer than were women with birth weights below 3000 g.

Although birth weight was related to breast cancer later in life, the link was no longer significant after accounting for birth length and head circumference. In contrast, birth length and head circumference remained significant predictors of future disease even after adjusting for birth weight.

Among infants of similar birth size, the researchers found that the gestational age at birth was inversely related to the risk of breast cancer.

These findings suggest that the hormones that influence body length and head circumference also play an important role in later cancer risk, Dr. McCormack noted.