Washington, Apr 19 : Breast cancer screening is effective, appropriate and reduces deaths from the disease in women aged up to 75 years old, and the best interval for screening is every three years, according to two studies.
The first study, which involved over 860,000 women aged 70-75, has been presented at the 6th European Breast Cancer Conference (EBCC-6) in Berlin, which showed that mammograms benefit women up to the age of 75.
The other study of nearly 100,000 women aged 50-62, also has been presented at EBCC-6. The finding of this study counters arguments that women should have mammograms more frequently.
Jacques Fracheboud, a senior researcher at the Erasmus Medical Center (Rotterdam, The Netherlands), and his colleagues found that from 2003, five years after screening was extended to women aged 70-75, there was a steady decline in deaths from breast cancer among women aged 75-79.
By 2006 breast cancer mortality was 29.5percent lower than the average for the period 1986-1997 for this age group - a time when breast cancer mortality in women aged 75-79 had remained stable. In 1986-1997 the average was 166 deaths per 100,000 women aged 75-79 and in 2006 it was 117 per 100,000.
It takes some years before a significant effect from screening can be seen, therefore breast cancer mortality was analysed for the ages 75-79.
"That means that women, aged 70-75 at the time that screening was extended to this age group, have become five years older and the reduction in breast cancer mortality shows that the screening has started to have a statistically significant effect," Fracheboud said.
Out of the 7.37 million screening examinations performed between 1998-2006, 862,655 were for women aged 70-75. Among women aged 50-69, 81.2 percent participated in the screening programme, and 71.9percent of women aged 70-75 took part.
However, the participation rate for these older women increased significantly during this period, rising from 62.5percent in 1998 to 77.6 percent in 2006.
In the 50-69 age group, 12.8 per 1000 women screened were referred for diagnostic assessment as a result of screening and breast cancer was detected in 4.5 per 1000, giving a positive predictive value (percentage of abnormal mammogram findings that were confirmed as breast cancer) of 36 percent. In the 70-75 age group, 16.4 per 1000 women screened were referred for diagnostic assessment and breast cancer was detected in 7.8 per 1000, giving a PPV of 47 percent.
"The difference shows that it is easier to find breast cancer in older women due to their breast tissue being less dense. But it is not necessarily an argument for continuing screening beyond 75 because many tumours found at this stage are slow growing and may never reach the stage of causing a problem. The results of our study suggest that screening women aged 70-75 has a strong impact on breast cancer mortality and that it is effective and appropriate up to 75 years," Fracheboud said.
In the second study - the UK Breast Screening Frequency Trial - researchers randomised nearly 100,000 women to have either an annual or a three-yearly mammogram after the date of the first screening to which they were invited after their 50th birthday.
After an average follow-up time of over 13 years (the trial started in 1989), there were 373 breast cancer deaths (out of a total of 49,173) among the study group of women invited to attend annual screening, and 374 (out of a total of 50,162) in the control group of women invited to three-yearly screening.
Among those women who actually attended the screening (as opposed to the whole group of women, including non-attenders), there were 209 breast cancer deaths in the study group and 231 in the control group. The researchers found no difference in mortality rates when they looked at only those cancers diagnosed during the three-year screening periods.
The absolute risk of dying from breast cancer was statistically insignificant between the two groups, with the control group having an absolute risk of only two per cent more than the study group.