Emerging Controversies in Breast Imaging: Is There a Place for Thermography?
We need further research to determine whether thermography has value for breast cancer screening.
By Gregory Plotnikoff, M.D., M.T.S., and Carolyn Torkelson, M.D., M.S.
For years, the medical community has sought to ascertain the benefits and limits of mammography as a screening tool for breast cancer. Nearly all North American medical organizations have supported mammography screening, although their recommendations have varied as to the age at which to begin. Recently, however, several leading medical journals have carried sharp criticisms of the effectiveness of mammography, with some authors questioning whether mammography should be recommended at all.1
In November of 2008, the Archives of Internal Medicine published a surprising study that has precipitated a major reconsideration of the value of mammography.2 Drawing from Norway’s large national database, the authors noted that breast cancer can regress and is sometimes not life-threatening, and suggested that use of routine mammography for breast cancer screening should be re-evaluated for those reasons.
In late 2009, the Journal of the American Medical Association (JAMA) published an editorial challenging the unquestioned value of mammography.3 The authors noted that “for every breast cancer death averted, even in the age group for which screening is least controversial (ages 50 to 70 years), 838 women must undergo screening for six years, generating thousands of screens, hundreds of biopsies, and many cancers treated as if they were life-threatening when they are not.”
In response to the JAMA editorial, Otis Brawley, M.D., chief medical officer of the American Cancer Society, was quoted in the New York Times as saying “the advantages of screening have been exaggerated.”4 He echoed what Ned Calonge, M.D., M.P.H., chair of the U.S. Preventive Services Task Force (USPSTF), had previously written: that mammography has been “oversold” to American women.5 By 2002, the USPSTF had already downgraded its recommendation for mammograms from “strongly recommend” to simply “recommend.”6 On November 16, 2009, the USPSTF issued new breast cancer screening guidelines based on review of all available data. The new guidelines recommend that women ages 50 to 74 years undergo screening mammography every two years. The guidelines also recommend against routine mammography screening for women before age 50, that screening end at age 74, and that physicians not teach women how to do breast self-exams.7
Prior to the new USPSTF guidelines and the JAMA editorial, more than 20 medical professionals and experts from Europe, North America, and elsewhere sent a letter to the editor of the London Times to ask that the British National Health Service rewrite its informed-consent pamphlet for mammography along the lines of one prepared by Peter Gotzsche of the Nordic Cochrane Collaborative.8,9 Research by Gotzsche and others has shown that the benefit of routine mammography has been exaggerated while the potential harm—that it could result in over diagnosis and unnecessary treatment of ductal carcinoma in situ, which poses no immediate threat to a woman’s life—has been downplayed.10,11
In 2009, both national and international experts have questioned the benefits of current mammography screening practices. At the same time, genetic screening is identifying more women at high risk for breast cancer, and those women are demanding more screening and imaging studies. Breast cancer awareness groups are also emphasizing the need for aggressive screening protocols for early detection and treatment. For those reasons, physicians need to be able to counsel women about the value of mammography and the current recommendations for it. They also should be aware that there has been renewed interest in alternative approaches to screening for and prevention of breast cancer, including thermography. This article describes breast thermography and calls for further research into its potential value.
Infrared imagery or thermography is a painless, noninvasive, relatively inexpensive technology that, like mammography, has FDA approval. Despite this, thermography has never been accepted as clinically useful by most cancer organizations, medical professionals, or insurance companies largely because of the insufficient evidence of effectiveness in terms of sensitivity and specificity. Nevertheless, nearly 50 years after its introduction, there is renewed interest in thermography, especially among practitioners of integrative or complementary medicine.
Thermography uses highly sensitive infrared cameras to detect subtle heat differentials emitted from the breast as infrared rays. The technology allows for detection of focal areas of physiologic change as noted by increased blood circulation and metabolic activity (Figure). This technological capacity may have clinical utility: In one study of 1,245 patients with suspicious, but not conclusive, thermograms, 38% percent developed cancer within one to four years.12 By tracking hyperthermic areas over time, proponents of thermography assert that it can detect precancerous inflammatory changes and cancerous tumors up to 10 years earlier than mammo- graphy.13 Accordingly, the interpretation of these images requires different techniques and skills. Interpreting mammograms is largely a matter of pattern recognition, whereas that is only one component of thermogram analysis. The other components are being able to quantitatively analyze temperature differentials, compare images over time, and gauge the autonomic response to a cold challenge.14
When thermography emerged in the 1960s, it was considered a key competitor to mammography and a technology that would decrease breast cancer mortality. That confidence was lost during the National Cancer Institute’s Breast Cancer Detection and Demonstration Project (BCDDP), which was initiated in 1973. After two years, project administrators removed thermography from the demonstration because of its disappointing results compared with mammography. Consequent to the end of the BCDDP, a consensus that mammography should be recommended as a means to reduce breast cancer mortality developed on the theory that it could detect cancerous tumors before they are palpable. Thus, treatment could be introduced earlier, presumably increasing the chances for survival compared with a later discovery of the disease. Thermography was addressed as a detection technology with great potential but insufficient evidence of effectiveness in terms of sensitivity and specificity.15 Although infrared fell off the radar, its supporters have continued to conduct research and develop protocols for testing the screening method and software for interpreting the images. These researchers are critical of the methodology used to conduct thermography in the BCDDP study, citing inconsistent procedures, protocols, equipment, and training of staff administering the screenings and interpreting the results.
Thermography enthusiasts now consider the technology to be an adjunct to mammography, not a competitor. This complementary approach arises from the basic difference in function between the two technologies: Mammography captures anatomical images, whereas thermography captures metabolic images.
One benefit of thermography is that it can be more effective than mammography for women with denser breasts, which means that it can be used on young women, women on estrogens, and women with significant fibrocystic changes. This advantage was confirmed in a 2008 New York Presbyterian–Cornell University study of 92 women recommended for breast biopsy based on mammography or ultrasound evaluations. The authors demonstrated that thermography found 58 of 60 biopsy-proven breast cancers for a 97% sensitivity, 44% specificity, and a 82% negative predictive value. The authors found the technology was helpful for women with dense breasts but not helpful for those who were morbidly obese or with breast size DD or greater.16
The Limits of Infrared Mammography
Although thermography holds promise, a number of questions must be answered before it can be recommended as a component of a breast cancer screening regimen.
The biggest question concerns the efficacy of thermography to detect breast cancer. Despite various studies that suggest positive results for thermography, there has never been a major randomized controlled trial to determine baseline measurements of sensitivity and specificity. It is hard to imagine thermography being accepted by the conventional medical establishment without such data or evidence of cost-effectiveness.17 In addition to questions about the effectiveness of thermography, research needs to be conducted to determine the cost of using it for widespread cancer screening.18
In its current state in the United States, thermography is a balkanized industry. Although thermography never took root in mainstream medicine, it has begun to flourish in alternative settings as a breast cancer detection service offered by some physicians, chiropractors, and naturopaths. In lieu of any industry or professional standards for thermography, a variety of practices and protocols have emerged among practitioners and equipment manufacturers. As one practitioner described it, the industry is in its “Wild West” days.19 This fragmented state weakens the credibility of the entire field because consumers have no way to distinguish credible from inferior thermographic techniques. As thermography emerges as an alternative screening tool, consumers are led to believe that it has been validated for efficacy and compared with mammography. This misconception could raise public-safety concerns.
Important barriers to widespread use of thermography include the lack of quality standards and the abundance of competing professional associations with varying degrees of training and accreditation in thermography screening. There is the International Academy of Clinical Thermology, the International College of Clinical Thermography, the International Thermographic Society, the American Academy of Thermology, the American Association of Medical Infrared Imaging, the American College of Clinical Thermology, and the American Chiropractic Board of Thermography. The multiplicity of organizations parallels the surfeit of names for the same process: thermography, thermology, digital infrared thermal imagery, infrared mammography, computerized infrared imaging, digital infrared imaging. Thus, although technology and protocols have markedly improved since the BCDDP in the 1970s, the fractionalization and marginalization of thermography means there are no universal standards for quality.
For thermography to even be considered within conventional medicine, or for practitioners to consider making referrals, questions about both fundamental research and methodology need to be addressed: Can it be used as a tool to assist patients in lifestyle modification for breast cancer? Could it reduce the need for expensive MR screening? Or, does it just open Pandora’s box? Could it actually introduce a more fearful state or increase demand for prophylactic mastectomy?
Additionally, a number of meth-odological issues would need to be addressed. First, for whom is it appropriate? Is it more appropriate for women within a certain age range? Is thermography equally effective among women with denser breast tissue and those who have had previous breast biopsies or surgical implants? Is it effective for women with all breast sizes and shapes? Is it effective for women on estrogens or anti-estrogens? Could it detect breast disease in men?
Second, what type of equipment should be used? The cameras currently used range from inappropriate low-end industrial cameras that were built to determine whether a building is well-insulated to expensive high-end cameras on par with those used on spy satellites. What standards does the industry need to set for optimal sensitivity and specificity, and for optimal cost-effectiveness?
Third, which protocols should be used? As with blood pressure readings for clinical research, accurate thermography readings require following standardized protocols. Should patients be subjected to a standardized cold challenge? Advocates say that it is necessary to get a thermal reading before and after the patient puts her hands in cold water. They say this stimulates an autonomic change, conserving the core body temperature by restricting the flow of blood to extremities, such as the breasts.14 The theory is that cancerous tumors do not respond to the cold challenge, thus providing a hot spot that is easier to detect. Other practitioners say a cold challenge is unnecessary.20
Finally, how should the images be interpreted? Since thermograms capture a physiological function rather than an anatomical structure, interpretation of these images may be difficult.21 Thus, both inter-observer and intra-observer reliability needs to be assessed. The same issue exists with mammograms, although this has been reduced somewhat by the implementation of strict accreditation practices for certification in breast radiology as well as the advent of computer-aided interpretation.22 At this time, there is no standardized and validated software for reading infrared images. Nor is there agreement on who should read them.
A woman’s lifetime risk of breast cancer was one in 12 in 1980; today it is one in 8. The ratio is even lower if one includes stage 0 (ductal carcinoma in situ). The recent JAMA editorial suggests we need a new focus and approach to screening if we are to reduce death and morbidity from breast cancer. If thermography is to play a role in this new focus, five questions need to be answered:
1. Could thermography be used to identify and differentiate significant cancers from those that pose minimal risk?
2. Could it reduce treatment for minimal-risk disease?
3. Could it be used to support informed decisions about prevention, screening, biopsy, and treatment?
4. Could it help identify the highest-risk patients and encourage them to engage in preventive interventions? and
5. Could it reasonably be used to monitor women at risk as an option to bilateral mastectomy?
Of course, to answer these questions, we would need funded clinical research based on validated methodologies.
We would also want to know if thermography could truly catch pre-cancerous lesions. If this could be documented, then thermography could provide additional value to women. However, protocols would need to be developed to differentiate a false-positive result requiring further (invasive or expensive) evaluation from early changes that could be reversed through lifestyle modification.
As more and more experts publicly challenge the value of mammography, we need to be exploring other technologies that may be more effective and cost- effective. Thermography has the potential to be very popular with patients for prevention and early detection as it is both painless and radiation-free. However, it should not be viewed as a replacement for mammography.
At present, we do not know if women who intentionally choose thermography over mammography are at significantly higher risk for premature mortality from undetected and potentially curable breast cancers. We also do not know if the test may help reduce mammography’s false-negative and false-positive rates. Could thermography better identify candidates for ultrasound-guided fine-needle aspiration of suspicious lesions? Could it relieve anxiety associated with recommendations for six-month follow up of suspicious mammogram findings? Likewise, could it reduce the need for the very expensive MRI analysis of suspicious lesions? These are questions that deserve attention. But few solo health professionals are in a position to advocate for a federally funded project to demonstrate the efficacy of thermography. Now, nearly 40 years after the 1973 BCDDP study, substantial advances in the technology mean that a reassessment of its clinical value and cost-effectiveness is warranted. For such potential to be realized, significant leadership is needed to establish both standards for quality and metrics for comparative effectiveness. If not from industry, from where will this effort come? MM
Gregory Plotnikoff is medical director of the Penny George Institute for Health and Healing at Abbott Northwestern Hospital. Carolyn Torkelson is medical director of the Women’s Health Center at the University of Minnesota and an assistant professor in the department of family medicine and community health.
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