Hamburg, Germany -- Many of today's generation of postmenopausal women have breast tissue more akin to that of younger women. This makes it harder for mammograms to pick up tumours or early signs of breast cancer in some over 50s and may also lead to unnecessary biopsies because of uncertainty in reading the results, a meeting of screening specialists will hear on Tuesday (16 March).
Mammogram samples from a screening programme in the Netherlands showed that a quarter of women aged 50 to 69 had the 'dense' mammographic breast patterns more normally associated with younger women. Among 50 to 54-year-olds the proportion was 44%.
Radiologist Dr Fred van der Horst said no one really knew why the change had occurred. It was unlikely to be due entirely to HRT as its use never exceeded 15% in the Netherlands. But, it could partly be due to the changes in childbearing patterns.
Dr van der Horst will be presenting the findings at the 4th European Breast Cancer Conference to a special meeting of the European Group for Breast Cancer Screening.
He said that breast cancer screening in postmenopausal women is effective but cancers can still go undetected. High mammographic density partly accounted for these missed cancers.
The study set out to see what impact breast density had on screening performance. Researchers chose a random sample of 2,000 from among the 54,500 women who are screened every two years in a screening programme. They classified the mammograms as dense if more than a quarter of the breast was composed of dense tissue. If less than a quarter of the breast comprised dense tissue the mammograms were classified as lucent.
They found that 25% of 50 to 69-year-olds overall had dense breasts – 44% of 50 to 54-year-olds reducing to 17% of 65 to 69-year-olds. They then calculated the ratio of screen-detected cancers to the total number of screen-detected cancers plus those cancers arising in the interval between screening, to estimate the sensitivity of the mammograms i.e. the ability of the mammogram to detect cancer accurately in those women that had it. In the dense group it was only 59% compared to 67% in the lucent group.
Dr van der Horst, a radiologist in the National Training and Expert Centre for Breast Cancer Screening in Nijmegen, said the difference in sensitivity between the two groups indicated the size of the potential problem.
"I don't think the problem of women referred on because of uncertainties over dense breasts is that big in the Netherlands as there is a low referral rate. But, if larger numbers of women are referred on, then the probability of referrals that turn out to be unnecessary in hindsight will increase, and the risk of unnecessary referral will be higher for those with dense breasts.
"However, it is difficult to disentangle the factors that play a part in referral as the chance of having breast cancer diagnosed increases with age anyway while the lower incidence in younger women is in itself a reason for a mammogram having a less certain predictive value."
Dr van der Horst said it was unlikely that HRT played more than a part in the fact that today's postmenopausal women had denser breasts than their counterparts 20 years ago.
"In the study group HRT use was under 10% in the perimenopausal period (the few years leading up to the menopause) and almost non-existent in the eldest group. In the Netherlands generally, HRT use has never been more than 15%. We know that women who have given birth have more lucent breasts than childless women. It's possible that demographic changes such as women having fewer children than 30 years ago and having them at a later age may play a role."
Can anything be done to improve screening detection in women with dense breast tissue? Dr van der Horst said there had been some research hinting that adding ultrasound to mammography could improve cancer detection in women with dense breasts, but there was not enough information to warrant its introduction on a large scale for screening purposes. There was a general consensus that in the under 50s there should be at most a year between screenings. It was possible that the current two-year screening interval for women between 50 and 55 was not optimal. However, more frequent screening in a population-based screening programme would influence cost-effectiveness and necessitate political choices.
Abstract no: 18 (The European Group for Breast Cancer Screening meeting is from 09.00 to 17.00 hrs in Hall 1).
 Dense tissue is glandular and shows white on mammograms. Lucent tissue is fat and shows black. The difficulty with dense tissue is that the white areas on mammograms may conceal possible cancer. Ultrasound acts the opposite way, showing cancerous tissue as black. In general women's breast tissue becomes more lucent as they age, especially if the have had children, although the denser a woman's tissue is when she is young the longer it takes to become lucent.
Materials provided by Federation Of European Cancer Societies. Note: Content may be edited for style and length.
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