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III - ALTERNATIVE BREAST CANCER SCREENING TESTS
1. Alternative tests for breast cancer screening
After looking at all available evidence, we came up with somewhat vague conclusion: if there is any benefit from mammographic screening, it is marginal at best. On the other hand, the risks and negatives are certain. If so, what Gøtzsche and Olsen said more than a decade ago did withstand the test of time: screening with X-ray mammography is not justified.
The question is: is there an alternative screening test that could help diagnose breast cancer early, with a better positives-to-negatives ratio?
Alternative tests to X-ray mammography for breast cancer screening come in two main flavors: those that use ionizing radiation, and those that don't. Obviously, these latter have the advantage of not exposing breast tissue to ionizing radiation, for which we have good reasons to believe it is potentially damaging even at the relatively low doses used for screening.
However, tests that don't use ionizing radiation are not necessarily entirely safe; and some are safer than the others.
Alternative tests using ionizing radiation
Not surprisingly, officially the most serious contenders for the alternative breast cancer screening test that use ionizing radiation, also use X-rays. But an entirely different technology, using gamma rays, has been recently developed into specialized breast cancer test. It is a possible accessory screening test, and some of its promoters argue it could be more than that.
The main - and quite general - objection to the standard X-ray mammography test (either film or digital) at this point is its questionable risks-to-benefits ratio. Data strongly suggests that the benefit of screening using this test limits to a small reduction in breast cancer mortality rate, bordering with statistically insignificant.
On the other hand, its negatives - mainly resulting from its insufficient accuracy (false positives, false negatives, overdiagnosis and overtreatment) - are undoubtedly significant and, by any realistic measure, larger than the positives.
In addition, it is unclear whether screening reduces or increases total mortality rate.
The radiation dose delivered by it is generally considered sufficiently low to be acceptable. This may be so at the level of average sensitivity to radiation, but not necessarily so for individual woman, whose radiation vulnerability may be much above the average. In any instance, a test that uses ionizing radiation could be considered viable alternative to the standard X-ray test only if it
does not deliver significantly higher dose of radiation and, at the same time, significantly reduces some of all of its negatives.
For a while, as the standard mammographic test was in its full swing as the one and only screening choice, there was little effort directed toward development of a possible alternative. However, as the questions about its actual risks and benefits started surfacing and taking hold, more and more attention was turned toward such alternatives.
The simplest one was already ongoing: digitalizing the standard test, by replacing film by a digital detector - digital mammography. This allowed for more efficient, computerized image processing, although no major improvements in screening efficiency were achieved. Digital conventional mammography probably somewhat reduces the average radiation exposure, but it comes at a price of much higher cost.
More complex X-ray alternatives, like tomosynthesis and breast CT (computed tomography), were also brought to the table. Both are based on the technology of constructing 3-D image from multiple 2-D images of the breast taken from different angles. The main difference in this respect is that the former takes 2-D images from directions that cover only a small fraction of a full circle around the breast, while with the latter 2-D images are taken from all directions, covering a full circle around breast.
Either produces generally higher quality image of breast tissue than the standard mammography (either film or digital). In addition, after the 3-D image is constructed, it can be computer-examined through tiny cross-sectional slices. It is hard to say, though, whether or how much it might improve screening efficiency. The drawback is that it would significantly prolong evaluation time vs. standard mammography.
Breast tomosynthesis requires mechanical apparatus similar to that of digital mammography, so the existing units can be modified for this new test type. That is an advantage relative to breast CT, which requires completely new machine, thus its introductory cost is higher. However, the absence of breast compression with it is definitely a plus.
Another type of detection test using ionizing radiation comes from nuclear medicine, and uses gamma radiation. It works by injecting radioactive isotope (tracer) into the bloodstream, which cancer cells tend to absorb at a significantly higher rate than normal cells. As a result, cancer cells emit higher level of radiation, which make them detectable on the images made with a special camera.
In general, these tests expose patients to much higher radiation dose than X-ray mammography.
Recent modification made to the standard technology is a breast-specialized test of this type - BSGI, BMI and PEM - which succeeded in significantly reducing radiation exposure, although it is still significantly higher than with X-ray mammography. Also, the procedure is more complex, more time consuming and more costly.
Alternative tests not using ionizing radiation
The first alternative test to X-ray mammography that does not use ionizing radiation is one that you most likely heard of as being not an alternative, but the most reliable evidence that we have strongly suggests the opposite. It is, of course, physical breast exam, which can be done either by a trained medical technician (clinical breast exam, CBE), or by a woman herself (breast self-exam, BSE).
There is no good reason not to combine the two.
It is obvious why these two tests were officially sidelined in the era of X-ray mammography domination. However, in probably the most meticulous, highest quality breast cancer random controlled trial - Canada 1/2 - there was practically no difference in breast cancer mortality between the population screened with X-rays, and population that used physical breast exam.
It is hard to believe that all the mambo-jumbo with X-ray mammography was actually unnecessary; worse yet, that it may have done more harm than good. But it as well may turn out to be so.
In addition to the physical exam, there are other alternative test that do not require exposure to ionizing radiation. Two breast cancer imaging tests commonly used to confirm or clarify mammography findings without additional exposure to ionizing radiation are breast ultrasound (also called sonography) and magnetic resonance imaging (MRI). Ultrasound is quickly developing technologically, and is very promising. The MRI is not likely to become a viable option any time soon, due to its high cost and uncertainties about the effect on health of the extremely strong magnetic fields it uses.
The third technique, somewhat obscured and different with respect to the type of information it provides, is breast thermography. At present, it seems that the special role of thermography in the screening process could be to indicate, based on the breast's blood vessel pattern, the level of risk of developing breast cancer within several years.
Finally, there is a unique blood test for cancer, which is not cancer-specific, but is highly accurate in detecting the presence of malignant growth somewhere in the body. It is the anti-malignin antibody screen (AMAS). Its usefulness is limited by it being non-specific, but the AMAS test certainly should be included in the set of accessory tests that can be used when appropriate.
Following pages give more details about these alternative tests to the standard X-ray mammography, beginning with the alternative tests using ionizing radiation.