The number of American women being screened regularly for breast cancer may be lower than has been previously thought.

An examination of a New Hampshire-based registry found that about one in three eligible women had never had a mammogram or had not had one in more than two years.

Most experts agree that women aged 40 and over should get regular mammograms. The National Cancer Institute recommends screening either annually or every two years. The American Cancer Society calls for annual screening.

Experts recommend regular mammograms in order to catch breast cancer at an early stage -- when treatment is more likely to lead to a cure. Many experts also recommend breast self-exams monthly along with annual physician exams to help detect any breast lumps that may be cancerous.

Read Web MD's "Learn More About Breast Cancer Screening."

Mammograms Decline With Age

Previous studies assessing the use of mammography screening have largely relied on patient self-reporting.

In an effort to get a more accurate picture of mammography use in the community, researchers from Dartmouth Medical School compared data from a New Hampshire screening registry to 2000 census figures for the state.

They found that 36 percent of women aged 40 and over had either never had a mammogram or had not had the test in more than two years.

Just two out of three women who had had a mammogram continued to be screened regularly, with twice as many of these women opting for annual screening than screening every two years.

Only about one in five women aged 80 and over continued to get regular mammograms.

Age alone should not be a reason to stop having regular mammograms, according to the American Cancer Society. As long as a woman is in good health and would be a candidate for treatment, she should continue to be screened with mammography, they say.

The study is to be published in the Oct. 15 issue of the journal Cancer.

Read Web MD's "Learn How to do a Breast Self-Exam."

Drop-Out Rate High

Researcher Patricia A. Carney, PhD, and colleagues concluded that “routine mammography screening may be occurring less often than believed when survey data alone are used.”

The overall use of mammogram screening in the study was 64 percent -- almost 20 percent lower than another study done in New Hampshire during the same period that relied on patient self-reporting.

But Debbie Saslow, PhD, of the American Cancer Society tells WebMD that the new figures seem to be in line with the national data.

“We believe that the number of eligible women who have regular mammography screenings is between 65 percent and 70 percent,” she says.

About a third of the women evaluated in the New Hampshire study who had had a mammogram did not continue to have them regularly. The researchers concluded that more research is needed to better understand why so many women don’t continue the practice. But Saslow says one main deterrent is obvious.

“Women tell us that the No. 1 reason why they haven’t been screened or don’t get regular mammograms is because their doctor didn’t tell them or didn’t remind them,” she says. “You get regular reminders from your dentist and even your veterinarian. But health facilities usually don’t remind women to come in for a mammogram because they lose money on screening. We are working to change that.”

Saslow says mammography screening trends have not changed dramatically in recent years. But she worries that women may find it harder to get timely screenings in the years to come.

That is because fewer doctors are specializing in radiology and fewer radiologists are doing mammography screening due to reimbursement and malpractice concerns, she says.

“So far we see shortages in only a few areas, but we are very concerned about the future,” she says. “More screening facilities are closing that opening, and there are warning signs that we may have an access problem in a few years.”

Read Web MD's "What Women Want to Know Before First Mammogram."

By Salynn Boyles, reviewed by Michael W. Smith, MD

SOURCES: Carney, P.A. Cancer, Oct. 15, 2005; vol 104: online edition. Patricia A. Carney, PhD, department of community and family medicine, Dartmouth Medical School, Lebanon, N.H. Debbie Saslow, PhD, director, breast and gynecologic cancer, American Cancer Society, Atlanta. American Cancer Society.