Is Tomosynthesis the Better Mammography Method?
Martin Lindner | 27-06-2016
Despite considerable controversy around the world, mammography has become the standard for the systematic early detection of breast cancer. New imaging technologies like tomosynthesis could usher in a new era of screening and help to develop a strategy for screening that is as rational and efficient as possible.
“Tomosynthesis is the Better Mammography Method”
The latest interim results of a large cohort study in Malmö, Sweden, suggest that breast tomosynthesis, a relatively new imaging process for the 3D depiction of the breast, could replace conventional 2D mammography in the future and thereby change the practice of breast cancer screening internationally.1 “Tomosynthesis is the better mammography method,” explains radiologist and senior author of the study Sophia Zackrisson of Lund University. “The method offers significant advantages, particularly for screening.”
Two-view digital mammography is currently the world’s gold standard for breast cancer screening. However, it is also known that this X-ray technique does not detect all breast tumors; in fact, up to one-third of all cancers may remain undetected, especially in women with very dense breast tissue.2 One reason for this is that overlapping breast tissue can cover tumors and thus prevent them from being seen on the 2D mammogram. With tomosynthesis, however, the X-ray tube moves in an arc over the breast, taking low-dose images across a range of angles. This imaging data is used to calculate one-millimeter-thin layers of the entire breast tissue. The layers are then displayed as a stack that the radiologist can scan through, rather like a flip book.
Not a Mix of Technologies, but a Rational Strategy
Studies done in the past few years have shown that more tumors are discovered when tomosynthesis is used in addition to mammography.3 However, the Malmö study has taken a different approach. “We did not want to simply add different technologies, but rather develop a strategy for screening that is as rational and efficient as possible,” states Zackrisson. The clinical trial, which began in 2010 in Malmö, was therefore designed from the very beginning to examine whether tomosynthesis is superior to mammography as a stand-alone procedure in the screening and could replace it as the standard method.
According to the preliminary results, this appears to be the case. An interim analysis of 7,500 of the planned 15,000 study participants shows that one-view tomosynthesis detects up to 43% more cancers than two-view mammography, and also reduces radiation exposure. Furthermore, the force needed to compress the breast could also be significantly reduced. “For many women, breast compression during the mammogram is very painful,” says Zackrisson’s colleague, Kristina Lång. It is therefore possible that tomosynthesis screening would also increase participation.
Outstanding Issues Should be Resolved in the Future
It remains to be seen whether the new method actually detects particularly aggressive cancers better. Another possible scenario is that the additional tumors detected are actually changes posing little risk, and that tomosynthesis could occasionally lead to overdiagnosis. One aspect that plays a role is that the time needed to assess tomosynthesis is higher due to the large number of slices displayed for each breast. In addition, the preliminary results show that more women needed to be called back for additional diagnostic testing to clarify the results. However, this recall rate increased in proportion with the cancer detection rate, which is consistent for the screening programs where the recall rate with 2D was already very low.
“We also observed that the recall rate, as well as the time needed to read the images, decreased with the doctor’s increased experience,” reports Lång. “There is apparently a significant learning curve here.” The definitive assessment of the procedure will be made in the years ahead, after the study has ended. The Malmö researchers also want to present a detailed analysis of the cost efficiency of the new methods.
The Growing World Market for Screenings
Breast cancer is the most common cancer in women worldwide, and the number of women affected continues to increase.7 There is thus a large need for early detection options. While breast cancer occurs extremely frequently in industrialized countries with Western lifestyles, the largest increase in disease rates is expected in less developed countries.8 By 2018, the total number of women worldwide who qualify for breast cancer screening could reach around 250 million.9
A driving force behind this development is the aging of the world population. It is well known that the probability of developing breast cancer increases with age. Also, a rising standard of living with greater educational opportunities for women results in later births and shorter lactation periods. This leads indirectly to a higher risk of breast cancer due to changing hormonal influences. China is therefore one of the largest markets for breast cancer screenings, along with the United States, Brazil, Japan, and Germany. China has experienced a rapid increase in disease rates since the early 1990s. Various regional screening programs have been developed in China since then. However, experts do not anticipate nationwide mammography screenings based on Western-style models in the near future. In fact, it is possible that ultrasound screening will play a role, as the procedure offers advantages for Asian women, who tend to have denser breast tissue and small breasts, and often develop cancer at an earlier age.10
While screening services are frequently offered by the private healthcare sector in emerging and developing countries like India, public screening programs are barely affordable in these countries.11 Cultural barriers can also stand in the way of breast examinations for early detection.12
On the other hand, in industrialized countries with organized screening programs, the services are paid for through taxes or by health insurance companies (sometimes with a co-payment from the patient) at predetermined rates. The total cost of the German mammography screening program, which screens around half of the women who are entitled to use the program, amounts to approximately US$200 million to US$250 million per year. That equates to about €70 or €80 per screening mammogram, including double reading, centralized quality assurance, and subsequent assessment examinations.13
An International Comparison of Screening Programs
In addition to enhancing screening methods, it is also very important to provide access to screening programs worldwide. According to a 2012 survey by the International Cancer Screening Network, more than two dozen countries worldwide have organized breast cancer screening programs.4 After the first pilot projects in 1977 in Japan, the approach spread to North America, Europe, and Australia in the 1980s and 1990s, and more recently to countries such as China, Singapore, Saudi Arabia, and some parts of Brazil.5 A global comparison shows differences as well as similarities between countries.
For example, women in the Scandinavian countries, the United Kingdom, and Germany receive a personal invitation for screening at predetermined intervals. In other countries, by contrast, participants are recruited through media campaigns or referred by their doctor. Screening programs are only available in certain regions of China, Saudi Arabia, Spain, and Switzerland.
One special case is “opportunistic screening,” in which women undergo the exam at their request or as part of routine medical care. Opportunistic screening plays an important role in the United States, for example. In Latin America, where there are national screening recommendations but no organized mammography programs, most screenings are performed at the patient’s request, and often by a private-sector doctor.6 The main problems with opportunistic screenings are that the necessary intense training for staff, and the quality assurance of imaging, image interpretation, and further work-up are not generally guaranteed to the same level as for organized screening programs. On average, this leads to higher risks of side effects and higher costs, without proof of a comparable effect.
Mammography is the standard screening technology around the world. It is sometimes supplemented by the doctor palpating the breast or examining it with ultrasound. Special centers, general medical facilities, and sometimes mobile screening units perform the examinations, primarily at two-year intervals. Many organized programs concentrate on patients between the ages of 50 and 70, but women are routinely screened starting at the age of 40 and after the age of 70 in Sweden, Australia, South Korea, Japan, and the United States. Participation rates also vary considerably: they stand at almost 20 percent in Japan and Saudi Arabia, at around 50 percent in Canada and Switzerland, and at over 80 percent in the Netherlands and Finland.
About the Author
Martin Lindner is an award-winning science writer based in Berlin, Germany. After completing his medical studies and a doctoral thesis on the history of medicine, he went into journalism. His articles have appeared in many major German and Swiss newspapers and magazines.
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