Washington, Apr 24 : Researchers have ruled out any association between breast cancer and induced abortion or spontaneous abortion (miscarriage).

Women younger than age 35 who carry a pregnancy to term appear to have a reduced lifetime risk of breast cancer. Pregnancy may accelerate breast cell differentiation, the process by which cells take on specialized roles.

“An incomplete pregnancy may not result in sufficient differentiation to counter the high levels of pregnancy hormones that may foster proliferation. However, these biological mechanisms are uncertain, and a prematurely terminated pregnancy may not affect breast cancer risk at all,” they said.

“We observed associations in two subgroups, an association between induced abortion and progesterone receptor–negative breast cancer [cancer that does not respond to the hormone progesterone] and an inverse association between spontaneous abortion before the age of 20 years and breast cancer incidence,” they added.

However, they caution that these secondary analyses are based on small numbers of women.

“No obvious mechanisms can be provided for these subgroup findings; thus, chance has to be considered as a possible explanation,” they wrote.

A 2003 international expert panel convened by the National Cancer Institute reviewed and assessed research regarding reproductive events and the risk of breast cancer, and concluded that based on existing evidence, induced abortion is not associated with an increased risk of breast cancer.

“Among this predominantly pre-menopausal population, neither induced nor spontaneous abortion was associated with the incidence of breast cancer,” authors concluded.

The report is published in the April 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. (ANI)