Switching Mammograms to Once Every 2 Years Could Come With Risks

WEDNESDAY, Nov. 27, 2019 (HealthDay News) -- Women who get mammograms every two years instead of annually might face a greater risk of being diagnosed with larger, later-stage breast tumors, a new, preliminary study suggests.

Researchers found that among 232 breast cancer patients at their hospital, those who'd undergone mammography screening every two years tended to have more advanced tumors: Of those 32 women, 44% were diagnosed with stage 2 or later cancer, versus 24% of patients who'd undergone annual screening.

The study did not look at the women's ultimate outcomes -- that is, whether annual screening reduced the risk of dying from breast cancer.

But the hope is to give women some information to consider when making screening decisions, said researcher Dr. Sarah Moorman, a radiology resident at the University of Michigan in Ann Arbor.

Those decisions are not necessarily easy. There are various guidelines on mammography screening, and they differ in the recommended start age, and how often women should be screened, Moorman pointed out.

For example, the U.S. Preventive Services Task Force recommends that women at average risk of breast cancer be screened every two years. The American Cancer Society, meanwhile, suggests yearly screening for women ages 45 to 54; older women can switch to screening every two years or stick with annual screenings.

It might seem like more-frequent screening would clearly be better. But there are also downsides to screening for any disease -- including "false positive" results that lead to further, sometimes invasive testing.

This latest study did not look at those potential "harms," Moorman said.

Dr. Richard Wender is chief cancer control officer with the American Cancer Society (ACS). He explained the rationale behind the ACS recommendations on mammography screening.

Overall, research suggests that yearly screening benefits women more, versus screening every two years -- in terms of catching tumors when they're smaller and avoiding more extensive treatment. But the advantage is somewhat less in women who are past menopause, compared with younger women, Wender said.

That's because although breast cancer is more common in older women, it typically grows and progresses more slowly after menopause than before. In addition, Wender explained, yearly screening results in many more "recalls" -- where women undergo further imaging after an initial mammogram looks suspicious.

And as far preventing deaths goes, Wender said that one trial has shown that annual screening can lower the risk of dying from breast cancer, versus biennial screening -- in women younger than 50.

"Given all of these findings," Wender said, "ACS recommended that annual screening is the best interval for all premenopausal women."

At age 55 -- a proxy for menopause -- women can either stick with yearly mammograms or switch to every other year, the ACS says.

"We do think the data are quite supportive that on a population level, screening every other year is optimal [for postmenopausal women]," Wender said.

But for individual women, he added, there are other factors they can consider and discuss with their doctor: If they have had an abnormal mammogram in the past, yearly screening might be wise. The same may be true if they have "dense" breasts with less fatty tissue -- which can make it harder to interpret the mammogram.

The current findings were based on 232 women, ages 40 to 82, who were diagnosed with breast cancer in 2016 or 2017. The vast majority, 200, had undergone yearly screening, while 32 women had been screened every two years.

On average, women in the biennial group had slightly larger tumors, and were less likely to be diagnosed in the earliest stages. In addition, 38% needed chemotherapy as part of their treatment, versus 28% of women in the annual-screening group; however, that difference was not significant in statistical terms.

According to Moorman, there were no clear differences between the two groups as far as age, race, family history of breast cancer, or the number who were "high-risk."

She will present the findings next week at the annual meeting of the Radiological Society of North America, in Chicago. Studies reported at meetings are generally considered preliminary until they are published in medical journal.

Wender said that screening guidelines will keep evolving as more research evidence comes in.

What's most important, he said, is that all eligible women get mammograms "at least every other year" -- with annual screenings being "ideal" for younger women.

Right now, Wender added, that's not the reality: Only about two-thirds of U.S. women in the screening age range get mammograms every other year.

More information

Susan G. Komen has more on breast cancer screening.