Hormones Have Both Positive, Negative Impact on Women's Colon Cancer
Posted on Thu, Mar. 04, 2004
Original story at newscientist.com.
Mar. 4 - Women who take estrogen and progestin after menopause develop fewer cases of colon cancer than their peers. But the cancers they develop tend to be more advanced when doctors find them, a new study says.
The report, in Wednesday's New England Journal of Medicine, is based on data from a major federal hormone study stopped in 2002 -- a sister study to the estrogen trial the National Institutes of Health publicly halted Tuesday. The findings underscore the importance of regular colon cancer screening for women older than 50, researchers say.
The paper also illustrates the promise doctors see in being able to compare the estrogen-progestin study against the just-stopped trial of estrogen alone, said Cheryl Ritenbaugh, a researcher with Portland's Kaiser Permanente Center for Health Research who worked on Wednesday's article.
Ritenbaugh said the results have two possible interpretations: The hormones could be affecting colon cancer biologically. Or they may be delaying cancer diagnoses.
If the estrogen-only study offers evidence of reduced cancer rates, "it would strongly support that something biological is happening" to the cancer, she said.
Colorectal cancer killed 29,000 U.S. women last year, behind only lung and breast cancers in deaths, the American Cancer Society estimates. Doctors would love to find medicines that prevent colon cancer in healthy people. Some hoped estrogen would fit the bill.
The study stopped in 2002 offers surprising and hard-to-interpret information about estrogen's effect on colon health. Scientists followed about 16,000 women, half taking the two-hormone drug and half a placebo. They found 48 colorectal cancers among women taking hormones and 74 among women on placebos -- roughly a 40 percent lower risk for hormone users.
But strange findings emerged when they looked at the individual cases. The two groups had cancers that, biologically, looked the same. But the cancer had spread to more lymph nodes, on average, in women taking hormones. And the two groups had roughly the same number of large cancers, Ritenbaugh said -- the women on hormones just had fewer small cancers.
Nine women on hormones died from colorectal cancer during the eight-year study period, compared with eight women on placebo.
That information could mean that the hormones are suppressing tumors, Ritenbaugh said, but are effective only against cancers that are very small and just forming, not more-established cancers.
Rates of bleeding and screening could explain the findings. Both groups of women had similar, lower-than-suggested rates of screening -- only 40 percent had a colonoscopy or sigmoidoscopy. But the women on hormones had much more vaginal bleeding than those on placebo. "Since the early sign of colorectal cancer was bleeding, and the women on the active drugs were bleeding," Ritenbaugh said, they may have ignored cancer symptoms as being hormone-related.
The estrogen-only study should help test that theory when more data is available in April and August, she said. Women in that study "had hysterectomies and didn't bleed," Ritenbaugh said, so there would be no masking of cancer symptoms. Women with uteruses do not get estrogen alone, because it can promote uterine cancer.
If it looks as if poor cancer screening causes the invasive cancers, Ritenbaugh said, "things like fecal occult blood tests would become more important in women on combined hormones, even for a little while."
If the hormones seem to biologically change small cancers, researchers would try to discern how that happens and whether colon cancer risks rise among women taking estrogen-fighting drugs, which are used to battle breast cancer.