Later-in-life babies may cut cancer risk.

Later-in-life babies may cut cancer risk

Women who bear their last child after age 34 face a significantly lower risk of endometrial cancer -- the fourth most common malignancy in U.S. women -- than do mothers who end their child-bearing much earlier, according to an epidemiologic study. For instance, the data reveal a risk reduction of as much as 60 percent for women who give birth after age 40 compared with those who bear no children after age 25.

The new findings support the prevailing view among cancer researchers that hormonal and reproductive factors play a role in the development of this malignancy, which begins in the endometrium, a membrane lining the muscular walls of the uterus. Endometrial cancer kills an estimated 4,000 U.S. women each year. Though its cause remains unknown, studies have indicated that obesity, hypertension, infertility, diabetes and late menopause appear to increase the risk of developing the cancer, whereas bearing many children reduces the risk.

Samuel M. Lesko and his colleagues at the Boston University School of Medicine in Brookline compared the reproductive histories of 483 women hospitalized for endometrial cancer and an age-matched group of 693 women hospitalized for conditions considered unrelated to reproductive factors (such as lung cancer and trauma). The analysis uncovered no indication that women who had never given birth faced an increased risk, or that a woman's age when she first gave birth affected her risk. However, as a woman's age at last childbirth increased beyond 25 years, her chance of developing the disease decreased steadily, the team reports in the March 15 AMERICAN JOURNAL OF EPIDEMIOLOGY.

The new data also support previous indications that endometrial cancer risk decreases as the number of childbirths rises. However, Lesko says the apparent protective effect of having multiple children appears independent of that conferred by late childbearing.

Early and late in a woman's reproductive years, her chances of failing to release an egg during the monthly ovarian cycle are much greater than in the intervening years. Oncologists generally believe that these anovulatory cycles increase endometrial cancer risk by exposing the endometrium to estrogen in the absence of progesterone, Lesko and his coauthors note. What remains unclear, Lesko says, is whether the apparent protective effect charted in the new study results from bearing children later in life, or just from maintaining the capacity to ovulate during each cycle.