Screening for breast cancer

Population based mammographic screening trials in the USA and Sweden have demonstrated a significant reduction in mortality in women who receive mammographic screening between the ages of 50 and 65 years of age. There is probably a similar but less pronounced risk reduction in women over 40 but experts are reticent concerning the recommendation of mammographic screening to women of younger ages, not least because of the albeit small radiation exposure to the active breasts in this younger age group.

 

In the UK, the mammographic screening programme, which is concentrating on once three yearly mammographic screening for 50-64 year old women, aims to achieve 25% reduction in the death rate from this disease over the next decade due to earlier diagnosis of the disease. Certainly the established trials showed that the screen detected cancers were of an earlier stage than clinically presenting ones. For example, in the Swedish trial more than 50% of screen detected cancers were less than 1.5 cm in diameter and more than 80% were axillary node negative (i.e the lymph nodes in the armpit were not affected when analysed under the microscope).

 

After an initial baseline screen, approximately 10% of women will need to be recalled for a subsequent analysis of some abnormality; subsequently once three yearly screening is considered sufficient (vide infra) in those with no abnormality.

 

Lobular cancers – vide infra - show up less well on mammography but other screening methods (ultrasound or MR) have not been validated in the way that has been accomplished for mammography.

 

With once three yearly routine mammography, it is predicted that 70% of all new cancers will be detected at a stage that is impalpable or small. The three year period of interval between imaging worries some but there will always be some ‘interval’ cancers that arise and grow fast and therefore clinically present in between screening points. In higher risk patients the interval may be brought down to once per year or bi-annually.

 

Women of younger ages are well advised to occasionally but regularly to feel their breasts and to report any discrete lumps. Genetic screening has already been mentioned and will be a topic of continuing debate for the patient and her sisters and offspring as the ease of genetic testing becomes greater and more genetic predisposition genes are discovered. Breast ultrasound is not a recommended method of breast screening by itself but may be a very useful adjunct to mammography and many centres are now using both methods together to improve pick-up rates. MRI imaging of the breasts is now a formidable competitor to mammography in the screening for breast cancer. The detection rates are as good as mammography in many series and the method has advantages in the young (where it is important to avoid unnecessary radiation exosure - however small - to the breast) and after breeast implant surgery.