Challenges and trends in breast cancer screening
The Rise of Mass Screening Programs
Breast cancer screening is currently a global standard of preventive medicine.1 Debates on the pros and cons have been raging since it was introduced in the early 1970s – and are far from over. Parallel to Western industrialized nations, interest in screening is also becoming increasingly common in countries such as China, Saudi Arabia, and Brazil. At the same time, new imaging technologies and the trend toward personalized care and treatment are gaining ground internationally. What does the future hold for breast cancer screening?
Screening mammograms have been a long-standing practice in North America, Europe, Australia, and Japan. “The strategy provides many important advantages,” confirms mammography screening expert Sylvia Heywang-Köbrunner, who recently contributed to the current position on the subject adopted by the International Agency for Research on Cancer (IARC).2 According to Heywang-Köbrunner, there is strong evidence that a significant number of breast cancer deaths can be prevented through regular mammogram screenings and more timely treatment.
Milestones of a Medical Paradigm
“Breast cancer screenings can be compared to other prevention efforts, such as those for high blood pressure or diabetes,” comments radiologist Ingvar Andersson from Lund University in Malmö, Sweden. One of the field’s pioneers, Andersson has been researching different screening exams since the 1970s and is currently working for the diagnostic company Unilabs, which is responsible for the screening program in southern Sweden.3
Andersson recalls that, in addition to the development of specialized X-ray devices and sensitive screen-film combinations in the 1960s and 1970s, the roots of this medical paradigm also lie in the Health Insurance Plan Study in New York. The long-term study, which began in 1963, showed the efficacy of mass screenings for breast cancer over an observation period of many years.4 Further randomized trials in Sweden and elsewhere confirmed the effect, and technology also improved, particularly with the introduction of digital mammography in early 2000. Today, more than two dozen countries around the world have breast cancer screening programs.
“Knowledge about breast cancer and the possibilities of screening are also much more firmly anchored in the minds of women,” adds Andersson. According to the latest IARC scientific paper, the risk of dying from breast cancer has dropped by more than 20% in areas where women have access to screening mammograms, and by as much as 40% among women who actually participate and undergo screening mammograms regularly.
The Problems of a Mass Screening Program
Nevertheless, the controversy about breast cancer screenings is by no means resolved. Some critics consider the benefits of comprehensive routine mammography outside clinical studies to be debatable.5 Others argue that the original large preventive effect of the screening has decreased in the last few decades. Because many breast cancer tumors can be treated more effectively today, very early diagnosis is no longer as important as it used to be.6
Even proponents of population-wide screening programs admit that the approach presents specific problems. For example, most women who take advantage of screenings do not develop breast cancer, but some may find themselves confronted with an inconclusive or suspicious finding in the initial screening mammogram – leading to a so-called recall.
Recalls and Overdiagnoses
Heywang-Köbrunner says it is estimated that on average one in five women who regularly participate in an organized mammography program for 20 years receives one recall during these 20 years. Most initial suspicions can be dispelled by a harmless additional test, such as another mammogram or an ultrasound examination. However, the uncertainty associated with these so-called false positive diagnoses can cause women a great deal of anxiety while they wait. “The psychological effects should not be ignored,” states Andersson.
“However, the most significant problem is overdiagnosis,” she adds. By this, she means tumors that would never be noticed without screening but once detected will typically result in surgery and radiation. Reasons why they would not have been detected include very slow tumor growth or early death from another cause.'
Estimates for the total number of overdiagnoses are difficult to determine and depend heavily on the defined period of observation. What is clear, though, is that for all women whose lives were saved by a screening, there were others who had to undergo treatment that in retrospect may have been unnecessary.
Trends and New Technologies
These difficulties can be partly remedied by new strategic approaches. “In the future, the screening will be more personalized than it is now,” predicts Andersson. He explains that the individual cancer risk is likely to be evaluated more precisely based on genetic analyses or biomarkers. This could then influence the type and intensity of the screening and help avoid unnecessary treatment.
Imaging technologies are also changing. Heywang-Köbrunner explains that breast tomosynthesis is an important innovation. The ability to view the breast in slices rather than as a single projection helps tumors to be detected more often and earlier, and to be more clearly defined.
“A combination of tomosynthesis and ultrasound in one and the same device would also be beneficial,” says Andersson. Such customized hardware could be very advantageous for efficient screening in women with dense breast tissue, for example.
Andersson also suggests another idea: Software for routine use in computer-assisted tumor detection. “One important barrier to mammography screening is a lack of competent radiologists prepared to read a large number of normal mammograms daily,” he says. “A computer-assisted detection (CAD) system that could rule out breast cancer with a high degree of accuracy and thus relieve radiologists from reading a significant proportion of screening mammograms would be highly desirable.”
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1Dowling EC, Klabunde C, Patnick J, et al. (2010) Breast and cervical cancer screening programme implementation in 16 countries. J Med Screen 17:139-46
2Interview with Sylvia Heywang-Köbrunner, Vienna, Austria, March 2, 2016
Lauby-Secretan B, Scoccianti C, Loomis D, et al. (2015) Breast-cancer screening – viewpoint of the IARC Working Group.
3Telephone interview with Ingvar Andersson, February 18, 2016
4Shapiro S, Venet W, Strax P, et al. (1982) Ten- to fourteen-year effect of screening on breast cancer mortality. J Natl Cancer Inst 69:349-55 Strax P (1984) Mass screening for control of breast cancer. Cancer 53(3 Suppl):665-70
5Jørgensen KJ, Zahl PH, Gøtzsche PC (2010) Breast cancer mortality in organised mammography screening in Denmark: comparative study. BMJ 340:c1241
Autier P, Boniol M, Gavin A, Vatten LJ (2011) Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: trend analysis of WHO mortality database. BMJ 343:c1241
Ciatto S, Houssami N, Bernardi D, et al. (2013) Integration of 3D digital mammography with tomosynthesis for population breast-cancer screening (STORM): a prospective comparison study. Lancet Oncol 14:583-9
6Welch HG (2010) Screening mammography – a long run for a short slide? N Engl J Med 363:1276-8