Breast scans less effective for some women

A study led by an ANU researcher has found that mammography is less effective for women who use hormone replacement therapy (HRT), who have had previous breast surgery and who are relatively thin.

Breast cancer is more difficult to detect and exclude in women with these three characteristics, according to Dr Emily Banks, a research fellow at the National Centre for Epidemiology and Population Health at ANU.

“Our results suggest that mammography may be less efficient, and possibly less effective at reducing mortality, in users of HRT, in women with previous breast surgery and in thin women compared with other women,” Dr Banks said.

"Mammography may be less efficient, and possibly less effective at reducing mortality, in users of HRT, women with previous breast surgery and thin women"

Dr Banks

“These women are also more likely than other women to have breast cancer diagnosed between screens.”

With colleagues from the United Kingdom, Dr Banks analysed the data of more than 122,000 women aged between 50- and 64-years involved in the UK’s Million Women Study.

“We analysed the effectiveness of mammography screening in each of these women and then referred to selected factors to better understand what contributes to women needing additional investigations after initial mammography (also known as “false positives”), and why breast cancer is diagnosed between screens in some women,” Dr Banks said.

According to the study:
• The sensitivity (the proportion of breast cancers that are detected at screening) of mammography for women using HRT was 83 per cent, compared to 92.1 per cent in women who had never used HRT.
• Women who had undergone breast surgery for a condition other than cancer had a sensitivity of 83.5 per cent, compared with 89.4 per cent in those who had never had breast surgery.
• In women who had a Body Mass Index (BMI) of less than 25, sensitivity to mammography was 85.7 per cent, compared with 91 per cent in women who had what is considered a healthy BMI, equal to or above 25.

The women completed a questionnaire about various personal factors and routines — including age, family history of breast cancer, physical activity, smoking and alcohol consumption — before mammography screening. Their health outcomes and breast screenings were followed over the subsequent 12 months.

Those factors found not to contribute significantly to the sensitivity and specificity of mammography were age, family history of breast cancer, past oral contraceptive use, tubal ligation, physical activity, smoking, alcohol consumption and education, according to the study.

“Women taking HRT need to be aware that it not only increases their risk of breast cancer, but also makes it more difficult to detect by mammography,” said Dr Banks.

The results of the study had implications for informing diagnosis and breast awareness, but should not dismiss mammography as the best way to detect breast cancer at an early stage, according to another of the paper’s authors, Dr Gillian Reeves.

“While these findings suggest that mammography may be more efficient in some women than others, it remains the best way of detecting breast cancer when it is still at an early stage,” Dr Reeves said. “These results highlight how important it is that, as well as attending for routine screening, women remain breast aware between screens.”

The full paper, Influence of personal characteristics of individual women on sensitivity and specificity of mammography in the Million Women Study: cohort study, can be found at:
http://bmj.bmjjournals.com/onlinefirst_date.shtml

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