Breast cancer screening is in the news once again. Late last year controversy flared around new recommendations in the frequency of screening. (A review of this change can be found Here.) Now it seems that even the type of screening available is generating controversy.
Current breast screening technology in the form of mammograms is a mature approach, the advantages and drawbacks have been extensively studied and are now quite well understood (though more is still being discovered, see the related article at the bottom of this post). As such we can use the mass of accumulated data to create guidelines that attempt to optimise how screening should be done. A balance must be struck between the benefits gained by accurate detection of cancer and the costs, both psychological and financial, of false positives generated by the screening process.
These are the points that must be kept in mind when evaluating new approaches for appropriateness in the consumer screening market. Recently the media has highlighted a minor battle between private medical industry, in the form of breast screening clinic Clinical Thermography, and professional medical organisations and cancer research and advocacy groups. Yesterday the NZ Herald ran a story about the clash, and you can see TV3 coverage Here*.
At issue is the offering of a breast cancer screening service using thermal imaging to detect incipient or established tumours in the breast. The operating principle behind this technique is the requirement of tumours to generate access to their own blood supply early in the process of formation in order to secure the nutrients required for the unrestrained cell growth that is typically associated with cancer.
This process is called angiogenesis and entails the formation of new blood vessels in and around the tumour. This brings a larger amount of blood to the area than would be seen normally and this blood would bring extra body heat with it. Given this information it is not unreasonable to attempt to use this physiological change to attempt to detect cancer. By using high resolution thermal imaging the surface temperature of the breast can be measured and used to infer the presence of “hot spots” that may indicate tumours.
Thermography is not a new technology, developed in the 1960s it was largely abandoned in the early 1980s after an influential trial found the false positive rate and sensitivity unsatisfactory. As such, while the approach is not novel there is a distinct lack of large scale trials from which we can determine the appropriate sensitivity and specificity to apply to the technique and thereby judge it’s efficacy in the screening market, especially using current technology. In particular the technique has been emphasised in the existing literature to have the most impact when used in conjunction with more understood approaches such as mammography.
The current halabaloo seems to centre around concerns by the medical community that the appropriate caveats will not be adequately conveyed to the public and thereby may lead to either unwarranted panic in individuals receiving false positive results or complacency in those that may receive false negative tests. In particular position paper put out by the Cancer Society et al. attempts to raise awareness that the thermography screening process does not have the data to allow the decisions regarding balance between benefit and harm mention above to be made effectively (a position echoed by the UK organisation CancerHelp UK).
In investigating this issue I visited the Clinical thermography website to see what they had to say about the relative effectiveness of Thermography and mommography. I found it revealing that on the FAQ page there were two questions addressing accuracy for Thermography and mammograms. The Thermography entry was essentially an apologetic giving reasons why thermography may give a false negative result, no numbers regarding sensitivity or specificity were included in this.Conversely the mammography entry was a condemnatory piece giving percentages of false negative for the two age groups of particular interest, without any further explanation.
The ommision of hard data in the Thermography portion of the FAQ may reflect the dearth of adequate information as decried by the position statement above or may simply be standard marketing tactics. Either way Clinical Thermography aren’t doing themselves any favours with this evasive approach. Now this is not to say that Clinical Thermography is wholly against mammography, they accurately state earlier in the FAQ that Thermography is not a replacement for mammograms and that the technique should be used in conjunction with other screening methods.
Interestingly an American site for Breast Thermography is careful to include a disclaimer on the front page of the website stating:
“Breast thermography offers women information that no other procedure can provide. However, breast thermography is not a replacement for or alternative to mammography or any other form of breast imaging. Breast thermography is meant to be used in addition to mammography and other tests or procedures. Breast thermography and mammography are complementary procedures, one test does not replace the other….”
This is a straight forward upfront statement that Clinical Thermography would do well to emulate on the front page of it’s own site.
Finally, I’d like to point out that the position I have taken in this post is not contested even by those who would be proponents of this screening method. A commentary piece, published in Minnesota Medicine last December, entitled “Emerging Controversies in Breast Imaging: Is There a Place for Thermography?” was essentially pro-thermography at least in terms of investigating the technique further in order to address the questions raised regarding it’s efficacy.
Quoting from the text of this article:
“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.”
“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.”
In addition, a study linked to on a pro-thermography website concluded:
“we currently limit the role of infrared imaging to that of a closely
controlled compliment to clinical exam and high quailty mammography. Our initial data should not be extrapolated to either formal screening or noncontrolled diagnostic environments without appropriate evaluation, preferably in prospective controlled multicenter trials.”
In summary, Thermography is at this stage a screening method of unproven efficacy. This is not to say that it could not become a valuable adjunctive tool in screening for breast cancer but that caution should be exercised by both promoters and customers of the technology not to oversell or over rely on the results obtained using this technique. Further research should be undertaken to determine the answers the the questions raised about the technique, namely accurate estimates of the sensitivity and specificity of the technique and what role in the screening process it is best suited for.
*This link seems to be down currently, but a note with regard to Breast Self-Examination (BSE) as mentioned in the TV3 story. This has also come under scrutiny as a practice that does not lead to improved outcomes. See the review of the new breast cancer screening guidelines linked to above.
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- The mammography wars heat up again (sciencebasedmedicine.org)