Screening: Many of today's generation of post-menopausal 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 European screening specialists will hear today in Hamburg.
Mammogram samples from a screening programme in the Netherlands showed a quarter of women aged 50-69 had the 'dense' mammographic breast patterns more normally associated with younger women. Among 50 to 54-year-olds, the proportion was 44 per cent.
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 per cent in the Netherlands. But it could partly be due to the changes in childbearing patterns.
Dr van der Horst will present the findings at the 4th European Breast Cancer Conference to a meeting of the European Group for Breast Cancer Screening.
Dr Ann O'Doherty, a consultant radiologist at St Vincent's Hospital, Dublin, and a board member of BreastCheck, the national cancer screening programme, said the findings should not deter women from presenting for screening. She said BreastCheck had a higher- than-expected cancer detection rate and the number of benign biopsies it found was "extremely low", much lower than in the UK screening programme.
"A mammogram does not pick up all cancers. We do not have a perfect test but we have picked up more cancers than expected," she said.
In 2002, the BreastCheck screening programme detected eight cancers for every 1,000 women who presented for screening. Some 38,242 women presented for screening and 306 breast cancers were detected. The number of benign biopsies was 57.
Dr van der Horst acknowledged breast cancer screening in post-menopausal women was effective but cancers could 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 per cent of 50 to 69-year-olds overall had dense breasts, 44 per cent of 50 to 54-year-olds reducing to 17 per cent 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 per cent compared with 67 per cent in the lucent group.