MONDAY, Jan. 5 (HealthDay News) -- Obese postmenopausal women who have never used hormone replacement therapy may face an increased risk of ovarian cancer, compared to normal-weight women, a new study suggests.

Interestingly, obese women who have used hormone replacement therapy (HRT) for symptoms of menopause may not face increased risk for this type of malignancy.

The study findings are published in the Feb. 15 issue of the journal Cancer.

The take-home message is a familiar one, experts said: Maintain a healthy body weight.

"This is another, very fine epidemiologic study that shows a relationship between obesity and female-related cancers," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "The two leading causes of cancer in the western world today are tobacco and obesity. We've made enormous progress with tobacco-related malignancies -- it's really stunning. The next wave is obesity-related illness."

Added Dr. Elizabeth A. Poynor, a gynecologic oncologist at Lenox Hill Hospital in New York City, "This is yet another health risk that we can talk about with women who are overweight, and yet another reason to lose weight."

Ovarian cancer is the fifth leading cancer killer of U.S. women and the leading killer among gynecologic malignancies. Only about 37 percent of women with this diagnosis will survive beyond five years, according to background information in the study.

Women who've had children and who've used oral contraceptives appear to have a decreased risk of the disease.

A family history of ovarian cancer along with HRT use is known to contribute to the risk, and there has been some evidence that excess body weight also ups the risk.

For the new study, investigators from the U.S. National Cancer Institute followed almost 95,000 U.S. women, aged 50 to 71, for an average of seven years.

Overall, obese women -- those with a body mass index (BMI) or 30 or above -- had a 26 percent higher chance of developing ovarian cancer than women of normal weight, a figure the researchers said was not statistically significant.

However, the picture was somewhat different among subgroups of women. Obese women who had never used hormone therapy had an 80 percent higher risk of developing ovarian cancer, compared with their normal-weight counterparts. There appeared to be no relationship between BMI and ovarian cancer among women who had used hormone therapy for menopausal symptoms.

Obese women without a family history of the disease had a 36 percent higher risk of developing ovarian cancer, although there was no heightened risk in obese women who did have a family history.

According to the study authors, the findings indicate that obesity may increase ovarian cancer risk through hormonal effects. Specifically, excess fat increases production of estrogen, which may spur the growth of ovarian cancer.

But the picture is likely much more complicated than that, said Dr. Michael A. Bookman, vice president for ambulatory care and clinical research at Fox Chase Cancer Center in Philadelphia.

Overall, obese women in the study did not have a notably higher risk for ovarian cancer. The increased risk was only seen in a subgroup of the women, he noted.

"When you do a subset analysis, there's always a risk," Bookman said. "They wave their hands and think maybe this is because estrogen is bad for you, but there are a lot of other things obesity does than create endogenous estrogen, like other growth factors.

"It's interesting that, in women who were exposed to menopausal hormones, there was some evidence that [hormones] actually protected them," he added. "It's, at best, a modest effect and not nearly as strong as the data with endometrial cancer. I'm not a fan of obesity, but I think, in this particular analysis, it's a pretty modest effect. It would be much more convincing if it were significant for the entire population."

Study lead author Dr. Michael Leitzmann, of the National Cancer Institute, said one "possible reason for the observation that obesity might lead to increased ovarian cancer risk in women who have not used HRT versus women who have is that exogenous estrogens supplied by menopausal hormones fail to add further to the high background levels of endogenous estrogens among obese women."

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