MedWire News: Researchers have found that high levels of a hormone released during early pregnancy may be responsible for the reduced long-term risk of breast cancer among women who have given birth.

Lead researcher Dr Annekatrin Lukanova, from the German Cancer Research Center in Heidelberg, and colleagues explain that women who have given birth at least once are, on average, 25% less likely to develop breast cancer than women who have never given birth. Furthermore, the risk of breast cancer falls with increasing number of pregnancies.

The protective effect becomes apparent several years following pregnancy is strongest when the first pregnancy occurred in the early reproductive life of a woman.

Although the reasons for this protective effect are not known, it thought that a pregnancy hormone called human chorionic gonadotropin may play a role.

To investigate further, the researchers studied 567 pregnant women who supplied blood samples for analysis during their first trimester, of whom 210 later developed breast cancer.

After accounting for age and other factors, the researchers found no overall association between human chorionic gonadotropin levels and breast cancer risk.

However, further analysis revealed that, after 14 years, women with the highest levels of the hormone in early pregnancy were 47% less likely to develop breast cancer than those with lowest levels of the hormone.

Writing in the American Journal of Epidemiology, Dr Lukanova and team conclude: “These findings, though very preliminary, are consistent with a possible long-term protective association of breast cancer risk with elevated levels of circulating human chorionic gonadotropin in the early stages of pregnancy.”

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