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Mammograms Not as Reliable for Younger Women

Denser Breasts, Fast-Growing Tumors to Blame
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WebMD Health News

Oct. 5, 2004 -- Women in their 40s may be advised to get mammograms -- but many tumors are missed, and too many women die. Breast density (thickness of breast tissue) and rapid growth of tumors when present among younger women are the primary reasons, a new study shows.

It's been controversial for years, whether women in their 40s actually benefit from screening mammograms. Statistics show that mammography reduces breast cancer deaths in older women, but it's been harder to prove that for younger women, says senior researcher Emily White, PhD, an epidemiologist and professor at Fred Hutchinson Cancer Center.

"Clearly for women over 50, mammography captures more cancers ... whereas for younger women, it misses a fairly good percentage of cancers," White tells WebMD. "This is the first study to examine all possible factors that could cause mammography to miss cancers in these younger women."

"Younger women should know that mammography will not necessarily find breast tumors," researcher Diana S. M. Buist, PhD, a scientific investigator with Group Health Cooperative in Seattle, tells WebMD. "For women with dense breasts, the best thing we can say there really needs be improved detection methods. This study underscores the need for more research."

Their study appears in the latest issue of the Journal of the National Cancer Institute.

Breast Density Biggest Culprit

In their study, Buist, White, and their colleagues enrolled 73 women in their 40s, and 503 women aged 50 and older. All had been diagnosed with invasive breast cancer within 24 months of a negative mammogram.

In the younger women, there were 13 "interval" cancers (detected within one year after negative mammogram) and 47 cancers caught on mammograms. In the over-50 women, there were 58 interval cancers and 359 screen-detected cancers.

Radiologists were careful to note breast density and quality of mammograms; they also factored in menopausal status, family history, hormone therapy, and body mass index (an indication of body fat), length of time since a negative mammogram, and certain aspects of the tumor cells.

Among the younger women:

  • 52% were diagnosed within 24 months of a negative mammogram, compared with 25% of older women
  • 28% were diagnosed within 12 months, compared with 14% of older women

Reasons for most missed cancers:

  • Among those caught a year or less after the mammogram, 68% were because of breast density.
  • Among those caught 24 months later, 38% were because of breast density; 31% were linked with faster growing tumors.

Difficulty getting a good mammographic image and difficulty in positioning the breast were the factors most strongly associated with these missed cancers, according to researchers. This was true among older and younger women with dense breasts.

What Should 40-Something Women Do?

"Young women who delay mammography for up to two years are putting themselves at great risk, because they have faster growing tumors," says White.

"It's true ... we see more young women [than older women] coming in between exams with new cancers," says Mary Newell, MD, a mammographer with Emory Healthcare in Atlanta. "Younger women tend to have denser breasts, and it's more difficult to find abnormalities on mammograms when breasts are denser. Also, younger women tend have more aggressive cancers.

"But Buist's study reflects exams done before 1994, and we've improved mammography technology since then," Newell tells WebMD. "Also, the screening guidelines have changed. We routinely screen women every year after age 40. This study confirms the need for women over 40 to get mammograms every year."

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