For women older than 50, having mammograms every two years instead of annually does not hurt their chances that breast cancer will be detected early, researchers reported yesterday.
But among women in their 40s, waiting two years was found to slightly increase the risk that the cancer will have progressed to a more dangerous stage when it is diagnosed.
The study does not address the larger question of whether women in their 40s should get mammograms at all. The benefit of screening for those women is relatively small, in part because breast cancer is less common at that age.
"But for those who choose to get them, we did see a benefit of having one every year," said Emily White, a researcher at Fred Hutchinson Cancer Research Center in Seattle, who conducted the study.
The ideal interval between screening mammograms, which are specialized X-rays, has never been determined. In this country, the American Cancer Society calls for annual mammograms, but the U.S. Preventive Services Task Force recommends having them every one or two years. In Europe, most countries recommend that women be screened every two years.
Mammograms can detect tumors too small for a woman or her doctor to feel. The hope is that a malignancy found earlier will be easier to treat and less likely to prove fatal.
To find out whether a woman screened every two years is more likely to be diagnosed with late-stage cancer - that is, a case that has already spread to her lymph nodes or to other parts of her body- White and others reviewed data on nearly 8,000 U.S. breast cancer patients: 2,440 who were screened every two years and 5,400 who got annual mammograms.
Their findings were reported in yesterday's issue of the Journal of the National Cancer Institute. Among women age 50 and older, there was no increase in the risk that breast cancer would be detected in the late stage if they were screened every two years. That's probably because postmenopausal women have slower-growing tumors, White said.
However, for women in their 40s, there was a small but significant difference: 28 percent of those who received biennial screening had late-stage disease when they were diagnosed, compared with 21 percent of those who got annual mammograms.
The Chicago Tribune is a Tribune Publishing newspaper.