Mammographic Screening for Breast Cancer

Fletcher S. et al NEJM, April 24, 2003, (348); Vol No 17: 1672-1680

Comment

Breast cancer is the commonest cause of cancer death in Australia. However, the leading cause of death in Australian women remains cardiovascular disease.

A recent review in the New England Journal of Medicine (NEJM) investigated the benefits of mammographic screening for breast cancer. Women aged 50-69 years who undergo mammographic screening have a statistically significant 20-35% reduction in mortality from breast cancer compared to women who are not screened. Although there were initial concerns raised in a 2000 review about whether mammographic screening did indeed save lives, the current review in the NEJM addresses the various concerns raised in the earlier 2000 review as well as reviewing all the currently available literature. The overall outcome remains that mammographic screening for women aged 50 – 69 years is beneficial and saves lives.

Controversy still remains in regards to screening women between the ages of 40-49. Review of all the clinical trial data shows that there is a 20% decrease in 15-year mortality from breast cancer in this age group through screening. Studies investigating this age group have suffered from potential biases. For instance, women entered into these trials in their late 40’s were likely to have had their breast cancer diagnosed in their 50’s with the benefit of screening being ascribed to the 40’s age group, when it should have been to the 50’s age group. However, a recent study published in the Lancet looked at the outcome of mammographic screening and mortality of breast cancer in the 20 years before and after the introduction of screening in Sweden. The outcome of this paper was that there was a clear benefit to screening women aged 40-49 every 18 months. They found a significant 48% reduction in breast cancer mortality, which represents a far greater benefit than has been reported in previous trials.

Mammographic service screening and mortality in breast cancer patients: 20-year follow-up before and after introduction of screening

Tabar L. et al Lancet, April 26 2003, (361); 1405-1410

Comment

This study compared the deaths from breast cancer diagnosed in the 20 years (1958-1977) before screening was introduced with those from breast cancer diagnosed in the 20 years after the introduction of screening (1978-1997) in two Swedish centres, one rural and one urban. A total of 210 000 women aged 20-69 years were involved in this study. The data was stratified according to age, with groups being analysed aged 20-39 and 40-69. In addition the specific age group of 40-49 was separately analysed. In this study only women aged 40-69 were invited to attend for mammographic screening, with mammograms being performed every 18 months in those aged 40-55 and 2 yearly after the age of 55 years. The compliance with breast screening through invitation was high as 85% of invited women participated in the mammogram screening program. Women under the age of 40 years were not invited for screening, but had screening mammograms for various other reasons.

The overall finding from this study was that the risk of death from breast cancer was reduced significantly by 44% in women aged 40-69 years who were invited to partake in the breast screening program as compared to non screened women. Even women who did not partake in screening also recorded a reduction in breast cancer mortality, although the magnitude of this reduction was less (16%). The improvement in mortality in this instance largely reflected better treatment modalities with the passage of time and women being more aware of abnormal breast symptoms and presenting earlier for medical assessment. There was no change in mortality in those aged 20-39 years. Importantly, in analysing the age group of 40-49 years, there was a clear reduction in breast cancer deaths in those who were screened as opposed to those not screened, with a reduction in breast cancer mortality of 48%. This was a significant finding as previous studies evaluating mammographic screening in this particular age group have not been able to demonstrate as significant a benefit to mammographic screening.

The overall finding from this trial is that screening mammogaphy does save lives and allows for earlier diagnosis and treatment of breast cancer. This translates into improved survival for women diagnosed with breast cancer.

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 Content updated November 11, 2003