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Breast Screening

Cancer screening - The principles

The World Health Organisation (WHO) defines cancer screening as "the systematic application of a test in an asymptomatic population, aiming to identify individuals with abnormalities suggestive of a specific cancer or pre-cancer, and refer them promptly for diagnosis and treatment." (1)

The WHO guidelines on screening were published in 1968, but are still applicable today. These classic principlesby Wilson and Jungner (2) include:



    Currently, there are four cancer screening programmes in place in the UK:

    1. NHS Breast Screening Programme 
    2. NHS Cervical Screening Programme  
    3. NHS Bowel Cancer Screening Programme
    4. Prostate Cancer Risk Management - an infomed choice programme

     

    Breast Screening

    Breast cancer accounts for nearly a quarter (23%) of all female cancers worldwide. In 2008, 1.38 milllion women were diagnosed globally. The lifetime risk of a female devolping breast cancer in the UK is 1 in 8, with 80% of cases arising in post-menopausal women (3). Breast cancer is extremely rare in women in their teens or early twenties and uncommon in women under 35. Although present treatment methods of surgery, chemotherapy and radiotherapy provide significant curative results, prevention and early detection is the best strategy to fight the disease. 

    The objective of an early detection programme is diagnosing cancer at its earliest stages when it is localized to the organ of origin, without metastasis to other organs or the surrounding tissue. Screening programmes therefore allow for a more favourable prognosis for patients, by offering increased and less toxic treatment options. This also enables the provision of services through more cost-effective modalities.  With the anticipated introduction of novel treatments and increasing cost of cancer therapy, breast cancer screening will become even more cost saving, particulary in a time of increasing budget cuts. (4) 

      There are three methods of screening for breast cancer:

      1. Breast self-examination
      2. Clinical breast examination 
      3. Screening mammography

      Although self and clinical breast examination are recommended adjuncts, screening mammography is the only proven method to effectively reduce mortality from breast cancer. The role and importance of mammography in the early detection of breast cancer has been well documented by many large-scale cohort studies.

      Thus, screening mammography is the basis of the NHS Breast Screening Programme (NHSBSP) which is going to be the basis of the remainder of this article. 

      Screening Mammography

      Mammography is an X-ray technique that was developed specifically for breast lesion examination.

      During the procedure each breast is placed in turn on the x-ray machine and gently but firmly compressed with a clear plate for a few seconds. Compression is needed to keep the breast still and to get the clearest picture with the lowest amount of radiation possible. Two views of each breast are then obtained; a Cranial - Caudal view and a Medial - Lateral Oblique view. 

      Image 1. Mammography: each breast is compressed horizontally, then obliquely and an x-ray is taken at each position. (5)

      The x-ray images are based on the different absorption of different types of breast tissue.

      A determinant of the sensitivity of mammography is the breast parenchymal density. Breast tissue changes with age and hormone levels. Density decreases with age as fibrous tissue is lost and replaced with fatty tissue. Tamoxifen therapy may also decrease breast density whereas combined HRT may result in increased breast density.

      Generally, the more fat there is in the breast, the easier it is to distinguish a mass or abnormality, which is the case in post-menopausal women. However, when the breast is dense, as with pre-menopausal women, the abnormality may be hidden in the tissue and additional investigations may be needed. In this case ultrasound and MRI are more applicable (4).

      Image 2. Digital mammogram: Right and left cranial-caudal views (1a), shows an area of assymmetry in the lateral right breast. The right and left medial-lateral oblique views (1b), show an area of asymmetry in the upper right breast (6).

       

      Digital mammogram (1a), right and left cranial-caudal views, shows an area of asymmetry in the later

      NHS Breast Screening Programme

      The NHSBSP was set up in 1988, and was the first of its kind in the world. It is now a world-renowned service, growing from strength to strength.

      WHO? 

      Women between the ages of 50 - 70 were originally invited to attend; an extension of the age range was introduced in 2010 which now includes women from 47 up to 73 years. Beyond 73 years old, women are not formally invited but they are encouraged to arrange for further screening if they wish. 

      WHAT?

      A two-view mammogram of each breast is taken as described above. The mammographs are then read by experienced radiologists and results sent within two weeks to the patients home and GP. Since 2010 mammography has been converted to a digital format, meaning all images are computerised and stored on file. This will hopefully increase the sensitivity and specificity of the procedure, allowing easier comparisons.

      WHEN?

      Women are invited to attend every three years. In between screening they are advised to remain "breast-aware" and if any changes or symptoms appear they should contact their GP as soon as possible. 

      WHERE?

      Depending on where the patient lives, it may be at a local dedicated clinic, hospital or mobile screening unit.

      WHY?

      The main aim is to detect any abnormalities on the mammogram. Approximately 5% of women will be asked to go to an assessment clinic for a further mammogram, either for technical reasons (if the picture was not clear enough) or because a potential abnormality was detected. At the assessment clinic, more tests may be carried out. These may include a clinical examination, more mammograms at different angles or with magnification, or examination using ultrasound. If required, a core biopsy to sample the breast tissue may be performed.

      PRO's & CON'S

      Although largely successful in the pre-clinical diagnosis of breast cancer and overall reduction of mortality, the NHSBSP has had some criticisms. Below is an overview of some of the advantages and disadvantages of the programme. 

      PRO'S

      • Regular screening has been shown by large cohort studies to reduce mortality from breast cancer. Between 2 and 2.5 lives are saved for every overdiagnosed case.
      • About 8 out of 1,000 women screened will have asymptomatic breast cancer.
      • Overall, around a third of breast cancers are diagnosed through screening.
      • Detection at a pre-symptomatic state results in earlier intervention and ultimately a greater prognosis.
      • If cancer is detected at an early stage treatment can be less invasive - patients are less likely to have mastectomy or chemotherapy.
      • A tailored approach has been implemented for high-risk groups. This includes MRI and genetic tests for these women, commencing at an earlier age. (3)

       

       

      Further statistics published by the NHSBSP can be found on their website at

      http://www.cancerscreening.nhs.uk/

      breastscreen/statistics.html

       

          CON'S

          • Despite all the cited benefits, it should be noted that mammography alone, with a false negative rate of 12%, is not an effective screening tool.(4) This false-negative rate is higher among younger patients. Therefore some cancerous lesions may go undetected and patients should remain "breast aware" with frequent self examination.
          • Lesions can be detected which actually turn out to be non-cancerous, creating false positives. Around 9% of women are recalled after their first screen but less than 10% of these will have either an in situ or invasive cancer.(3)
          • It involves radiation exposure, which is itself carcinogenic. For every 14,000 women screened regulary for 10 years, one will develop breast cancer and will die because of the radiation exposure.
          • The screening process may cause anxiety and worry to some women, particularly so if a false positive arises.
          • Certain groups and communities are not engaged with the programme. Invitiation requires registration with a GP and research shows that black British women have a higher mortality as diagnosis is generally late. There is a need for more effective communication towards these women and this has been implemented by the NHSBSP.

          Outcomes and the Future

          Since the introduction of the breast screening programme in 1988, incidence rates have continued their upward trend. Along with many other factors, this rise may reflect the higher pick-up rates of cancer that may have went undiagnosed in many patients. 

          Earlier detection and improved treatment has meant that survival rates have also risen. Survival rates from breast cancer is much better than many other cancers. 

          Therfore, overall it is easy to see that breast screening is a very important programme in the fight against cancer. With new imaging techniques and the targeting of high risk groups and also women who are unlikely to pursue the screening, hopefully these mortality figures will drop even further. 

           

          Figure 1. Malignant breast cancer incidence (A) and mortality (B) in white and black women in North America. (7)

          References

          1. WHO. Cancer. Fact sheet N°297. February 2012. Available at URL: http://www.who.int/mediacentre/factsheets/fs297/en/

          2. Wilson JMG, Jungner G. Principles and practice of screening for disease. Geneva: WHO; 1968. Available at URL: http://whqlibdoc.who.int/php/WHO_PHP_34.pdf

          3. NHS Breast Screening Programme website. 2012. http://www.cancerscreening.nhs.uk/breastscreen/index.html

          4. EMRO Technical Publications Series 30. Guidelines for the early detection and screening of breast cancer. Oussama M.N. Khatib, Atord Modjtabai. World Health Organization 2006. Available at URL: http://www.emro.who.int/dsaf/dsa696.pdf

          5. University of Maryland Greenebaum Cancer Centre, Breast Evaluation and Treatment. Available at URL: http://www.umgcc.org/breast_program/mammography.htm

          6. JeongMi Park MD, Megha Garg MD, Laurent Grignon MS, Laurie L. Fajardo MD, MBA. Breast Imaging: Entering the Electronic Era. Imaging Economics. December 2005. Available at URL: http://www.imagingeconomics.com/issues/articles/2005-12_04.asp

          7. Saving Women's Lives: Strategies for Improving Breast Cancer Detection and Diagnosis.Institute of Medicine (US) and National Research Council (US) Committee on New Approaches to Early Detection and Diagnosis of Breast Cancer; Joy JE, Penhoet EE, Petitti DB, editors.Washington (DC): National Academies Press (US); 2005.Copyright © 2005, National Academy of Sciences. Available at URL: http://www.ncbi.nlm.nih.gov/books/NBK22316/

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