WASHINGTON (Reuters) – Women who never got mammograms are far more likely to die of breast cancer than women who are regularly screened, US researchers reported this week.

They said 75 percent of the women they studied who died of breast cancer had never had a mammogram, or were diagnosed after their very first mammogram. Only 25 percent of the women they studied who died of breast cancer had received more than one mammogram.

"The most effective method for women to avoid death from breast cancer is to have regular mammographic screening," Dr. Blake Cady of Cambridge Hospital Breast Center and Harvard Medical School in Massachusetts told reporters in a telephone briefing.

"Women who are in screening programmes have only a 4.7 percent mortality. Women who are not screened have a 56 percent mortality," added Cady, who will present his findings later this week to a meeting of the American Society of Clinical Oncology.

"That is the same as the overall mortality we used to see in breast cancer up to 1970, prior to the onset of wide mammography screening."

A mammogram is an X-ray of the breast that can spot tumours before they are large enough to feel, and potentially before they spread. Cady and colleagues examined 6,997 Massachusetts breast cancer patients, some who got regular mammograms and some who did not, between 1990 and 1999.

The patients were followed through 2007.

After about 12.5 years of follow-up, 461 of the women died of their breast cancer. Nearly 75 percent of these were women who had not had regular mammograms.

Cady said it is not clear why some women did not get mammograms and said it is possible these women got less medical care in general. "We didn't pretend to understand the reasons for not getting mammograms," he said.

People who are ill, who do not speak English or who are poor could all be among those not getting regular medical care and thus not getting mammograms, which in the United States are recommended for all women over the age of 50. There has been some debate about the value of mammograms. Most cancer societies and many governments recommend that women be screened regularly. Breast cancer kills more than 400,000 women a year globally.