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III - ALTERNATIVE BREAST CANCER SCREENING TESTS
Non-ionizing-radiation (NIR) tests for
|2 good choices to prevent breast cancer|
III - ALTERNATIVE TESTS
▪ False positive
▪ Screen exposure
▪ Radiation risk
Alternative tests to the X-ray mammography for breast cancer screening come in two main flavors: those that use ionizing radiation, and those that don't. Here we'll look at the latter. 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).
The third technique, somewhat obscured and different in the type of information it provides, is breast termography.
Let's start with the first two, breast ultrasound and MRI. Either is more sensitive than mammography, but neither is seriously considered as an alternative for breast cancer screening. Why not?
With MRI, one important reason is the
cost. A single session
averages $2000-4000 (with and without contrast agent,
respectively), which is
10-20 times the average cost of the standard X-ray mammography session. Another drawback of MRI - a price to pay for its higher sensitivity - is significantly more false positives than with mammography, which is already too much.
In addition, the procedure is contraindicated for more than a few individuals, including those allergic to the contrast agent, claustrophobic, those that for any reason have difficulty to lay still through the lengthy procedure, those with pacemaker (which can be affected by MRI's strong magnetic fields), and those with metallic implants.
Also, it is uncertain how the highly intense electromagnetic fields produced by MRI scanners can affect health. While no ill short-term effects resulting from MRI scans have been directly observed, there is insufficient research data to conclude that there is no possible adverse effects longer term. In fact, magnetic fields are listed among 216 breast carcinogens in a recent comprehensive report.
Static magnetic fields produced by MRI can be extremely strong, more than 100,000 times stronger than Earth's magnetic field. Most MRI systems today operate below 3T (T=Tesla) static field, which is still
tens of thousands times stronger than Earth's magnetic field;
caution is certainly advisable. Human body has its own, subtle magnetic field, which changes with the state of health; it is certainly affected by the exposure to much stronger MRI field; we only don't know how, and how that does affect body functions.
Commonly, we can hear statements from the professional medical circles that static magnetic fields in general, and those produced by MRI scanners in particular, are benign. Considering that no reliable study exist supporting this view, it is only opinion, at the best, and one that is not shared by everyone. In the initial draft of new EU power field legislature, occupational exposure to static magnetic field was limited to 2 Tesla (T, unit for magnetic field strength, equaling 2,000 Gauss); it was later dropped because of the combination of pressures and uncertainty, but some form of future restriction to field strength applied in medical diagnostic procedures (and non-occupational exposures in general) level is likely.
no one really knows what the possible effects on health from exposures to high-intensity static magnetic fields could be.
What we do know, is that magnetic fields, both static and pulsating, if properly applied, can have therapeutic effect on relieving or eliminating various forms of pain and degenerative processes, including cancer. And that alone justifies caution, because
anything that has
the power to cause positive effect,
also has the power to cause negative effect.
One example of the negative effect is the well documented ill effect of magnetic field exposure on the increased risk of childhood cancer - particularly leukemia - due to exposure to comparatively quite weak pulsating magnetic fields produced by power lines.
MRI magnetic fields are of much higher intensity than those used for therapeutic purposes, which is not necessarily good, nor bad; we have sufficient evidence to conclude that biological effects of power fields do not "comply" with the simple dose-response scheme. The effect of any specific form of power fields on cellular health
depends on the multitude of interacting factors,
which in addition to field intensity include frequency, variability, presence of other power field forms, presence of specific internal or external chemicals and, of course, individual sensitivities. Exposure may have adverse effect at some specific lower, and no effect at some specific higher intensities/frequencies, or vice versa.
The fact is that magnetic field of just about any intensity level is potentially capable of interfering with extremely subtle electrical circuitry of the human body.
It doesn't make it any simpler that MRI scans also produce very intense electromagnetic (radio-wave) radiation, as well as so called gradient magnetic fields that can change thousands times per second.
The frequency of MRI radio-wave emission depends on its static magnetic field strength, as 42.57 MHz per tesla (so called resonance frequency for proton, i.e. positive hydrogen ion). With most MRI scans working in the 1-5T range, the corresponding radio frequencies are in 40-200 MHz range. This is the range of very high (radio) frequencies, or VHF, which is followed by ultra high frequencies (UHF), with the typical cell phone frequency level at about 1,000 MHz. Since adverse biological and health effects have been indicated for exposures to both, lower and higher radio frequencies than those emitted by MRI scanners,
their emission cannot be assumed harmless.
As already mentioned, the MRI radio emission is also very intense, to the point of being capable of inducing hyperthermia (elevating the temperature of body tissues).
Possible longer-term health effects of the quickly changing gradient magnetic fields in an MRI scan are also poorly understood. In the modern MRI machines, high-frequency gradient fields needed for higher resolutions are strong enough to cause peripheral nerve stimulation. Other, more subtle sensation-wise and possibly adverse forms of effects on cellular functions cannot be excluded.
In short, despite its imaging superiority, MRI is not a viable alternative for the principal test in a breast cancer screening program. For the same reasons - high cost, high rate of false positives, and uncertain long-term effects on health - it is not a candidate for the test of choice for individual periodic breast screening as well.
And what about ultrasound? It is used in medical imaging for over half a century. Presently, with the MRI and biopsy, it is used whenever it is necessary to clarify or confirm mammographic test. It has higher sensitivity than mammography, while comparable cost and time expenditure. Unlike mammography, it scans the entire breast and does not have its accuracy compromised by high breast density, does not require breast compression, and uses generally safer, non-ionizing form of radiation.
Why don't we just use ultrasound for screening asymptomatic women for signs of breast cancer?
Probably more than anything else, it was the result of public perception which, in turn, was a product of the fairly random activity that happened to be selectively promoting X-ray mammography. Perhaps, at least in part, due to the X-ray imaging being prevailing diagnostic imaging method in general, and particularly back in the 1970s. As B. H. Lerner states, medical technology historians generally agree that the social perception of new medical technologies is not necessarily based on the facts, as much as
on the opinions of those that happened to get the upper hand
in their introduction to public.
(Background Paper for the Institute of Medicine report: Mammography and Beyond: Developing Technologies for the Early Detection of Breast Cancer, 2001).
It certainly fully applies to the advance of X-ray mammography screening, as well as the relative obscurity of ultrasound.
Unlike X-ray mammography, which emerged as the accepted and practiced method of screening as a result of more than a decade of committed support by some researchers, radiologists and organizations - from technical improvements by Egan in the late 1950s, to Zuckerman and Strax (the latter initiating the landmark HIP screening trial that seemed to had proven both, earlier breast cancer diagnosis and significantly lower mortality for the screened population, the former seemingly confirmed by the following Breast Cancer Detection Demonstration Project in the mid 1970s) and, finally, the push by two major organizations, American Cancer Society and National Cancer Institute, for which the "effective" screening was just what doctor ordered for their newly intensified "war" on breast cancer - culminating in an enthusiastic, persistent public campaign,
ultrasound never got similar support needed for such a lift off.
Consequently, it was left where X-ray mammography itself once was: as a mere diagnostic tool. Moreover, in the course of X-ray mammography screening advance, ultrasound as a possible breast cancer screening method inherited an a priori dismissive view, just the opposite of that given to mammography:
negatives were exaggerated,
and advantages downplayed or neglected.
It was looked down at as a possible alternative, yet it was, at the same time, used as an accessory test to X-ray mammography screening.
What are the negatives of ultrasound as a screening tool for breast cancer? Until recent, ultrasound imaging had two diagnostic drawbacks vs. X-ray mammography. It didn't have that high degree of repeatability and, due to its higher sensitivity, had significantly more false positives.
Difficulties to achieve repeatability of test results were not stranger to X-ray mammography as well. Even after Egan improved its technical aspects, it took years of hard work to develop methodology that would insure acceptable level of repeatability. It is very likely that similar effort would have resulted in a comparable - or better - repeatability with the ultrasound mammography as well. But, being labeled as "inferior" by the mainstream medicine, it was never given that chance.
In the meantime, technological advances nearly eliminated the need for developing laborious specialized, unified methodologies for ultrasound breast testing, or sonomammography; more about it in a bit. It also reduced the rate of false positives, although it will likely remain higher than with X-ray mammography. That, however, should be partly offset by its likely lower rate of false negatives, making the overall difference in this respect relatively small.
On the other hand, significant reduction in the radiation risk favors ultrasound. Sound waves are mechanical waves, usually in the 3-10 MHz frequency range (sound waves over 20,000 Hz, or 0.02 MHz, are ultrasound, inaudible by humans), with resolution generally increasing with the frequency. These waves are significantly less invasive to biological tissues than ionizing electromagnetic radiation. Although they also can produce slight tissue heating, pressure, and may enhance inflammatory response, their effect on body's electrical circuitry - hence on cellular homeostasis - is comparatively negligible.
Most importantly, unlike X-rays, ultrasound waves
reach energy level needed to cause
direct damage to the DNA.
Due to technological advances, sonomammography has reached the level at which it compares favorably to X-ray mammography as a screening test of choice. This advance evolves along two lines:
(1) making the procedure automated by replacing manually handled transceiver with some form of a fixed breast cover, and
2) by enhancing video output (color, 3-D images. etc.).
Breast ultrasound is turning into fascinating technology, which in addition to supplying detailed images of breast tissue structures, is also capable of assessing blood supply in suspicious breast structures (Doppler ultrasound), as well as discerning harder, stiffer diseased tissue from softer, more elastic healthy tissue by detecting their change before and after slight pressure, which can be induced either mechanically, or by additional, low-frequency ultrasound field (ultrasonic elastography, or sonoelastography).
In 2006, Dr. Richard Barr from NE Ohio Universities College of Medicine reported initial experiment on 59 patients in which their ultrasonic elastography technique correctly identified 16 out of 16 invasive and 56 out of 56 benign breast cancer tumors, for 100% sensitivity (efficiency in detecting disease when it is present, defined as P/D, where P is the number of positive test results within the group that has the disease, and D the total number of tested cases in that group) and specificity (efficiency in detecting the absence of disease, defined as N/F, where N is the number of negative test result within those free of disease and F the total number of disease-free cases tested).
Another trial by Dr. Barr's team, on 80 patients with 123 lesions, accurately detected all 17 malignant lesions and 105 out of 106 benign lesions, for 100% sensitivity and 99% specificity.
The following multi-center trial confirmed high test sensitivity (98.2%), but its specificity averaged 85%. Lower specificity was probably the result of varying level of training of radiologists in the six participating centers. But even those figures
compare favorably to the standard X-ray mammography,
Knowing that the false positive rate of a test is given by 1-specificity (or 100-specificity in percents), implies that with this new, improved technology, ultrasound can have
about as high, or lower rate of false positives, and significantly lower rate of false negatives
(given by 1-sensitivity) than the standard X-ray mammography.
Elastography is experimenting with different detection criteria: Dr. Barr uses lesion size comparison between regular ultrasound and elastography, some researchers use color enhanced imaging with Dr. Ueno's color classification system (color-coded enhanced imaging, where colors are specific to a certain level of tissue stiffness), or simply a nominal stiffness criteria with gray scale imaging. The results vary somewhat with the technique and experience, but generally are
comparable or superior to X-ray mammography.
With further refinements, it is very likely that sonomammography using elasticity imaging will soon become clearly superior to X-ray mammography.
Sonomammography alone also becomes comparable or superior to mammography in the detection efficacy. Thomas Nelson from University of California, San Diego, has encouraging results in developing a volume breast ultrasound scanner (VBUS) for early breast cancer detection with 3-D ultrasound tomography. September last year, U-System from California was cleared to market their Automated Breast Ultrasound system (ABUS) for screening asymptomatic women in the European Union, and so on.
In short, despite being sidelined for decades, breast ultrasound seems to be on the short course to become clearly superior breast cancer test to X-ray mammography.
In light of this, it becomes evident that focusing on the standard X-ray mammography as the breast cancer screening method of choice for over three decades
was not justified by its de facto safety and efficacy.
Unfortunately, X-ray imaging in general is all to some (influential) people: the traditional method in medical practice, official icon and dominant imaging industry. Many careers, prestige and big profits, depend on its prolonged use, and that significantly slows down development and acceptance of the alternative methods, such as ultrasound. Nevertheless, the progress toward better and safer technologies is underway, and it will be hard to stop.
Risk assessment: thermography
All major breast imaging technologies use one or more agents foreign to the body - be it X-rays, gamma radiation, with or without contrast agents, or ultrasound - to penetrate the tissue and produce its image. That is, all but one. The technology capturing breasts own thermal emission, so called thermography,
can reveal changes in the thermal blueprint of the breast indicative of abnormal tissue formation much sooner than any other.
As soon as an invasive tumor becomes active, it starts forming blood vessel structure to increase its blood supply. The increased blood concentration around it results in more intense thermal emission from this area, that can be detected years before tumor grows large enough to be detected by mammography, ultrasound or MRI.
Not every deviation in breast tissue's thermal pattern is the result of a cancerous growth or, if it is, will necessarily progress further. Hence, thermography is not a diagnostic tool; its main purpose is
Based on breast's thermal patterns, thermologist determines breast cancer risk potential based on the 5-level scale, from the lowest (TH1) to the highest (TH5). According to The Thermogram Center, research data indicates that 40% of those with high or highest risk thermograms (TH4 and TH5) develop active cancer within 10 years.
That makes a high-risk thermogam by far
the most significant breast cancer risk factor,
justifying additional testing (even if nothing suspicious was found with a recent mammogram, ultrasound or MRI) and, if it turns out negative, adopting a continuous, comprehensive strategy for minimizing breast cancer risk.
Putting it all together, it seems safe to suggest that public screening based on breast ultrasound, combined with more widely spaced in time breast thermograms, would provide at least as much of the early detection benefit as X-ray mammography, but with significantly lower risk factor. Whether or not those in charge of public policy will follow up in this direction remains to be seen.
Among possible obstacles to such a move are new imaging techniques based on ionizing radiation. Some of them do have certain advantages over the standard X-ray mammography and, being still in the traditional radiologic diagnostic groove, may be preferred by the establishments for that reason.
And there is yet another angle to it. Is there a test that would cover all the cancers, not only that of the breast? Sounds too good to be true but, in fact - there is such test. It is called anti-malignin antibody screen or, for short, AMAS. Although often referred to as "new test", it is about as old as X-ray mammography: FDA approved it for cancer screening as far back as 1977. More about it on the next page.