Mammography may be taking the back seat in the future
Not quite ready for prime time-- but on its way-- is the liquid biopsy, a blood test that detects minute amounts of cancer markers well before a tumor could be detected on a mammogram. In recent studies, it appears that sensitivity and specificity of these early liquid biopsy assays appear competitive with mammography already.
As we all tout the saying, “The earlier we catch it, the better the outcome”; liquid biopsies could revolutionize breast cancer treatment programs since it is conceivable that we would be aware of the cancer long before we typically are able to intervene now.
In addition, assuming that the blood test is cost effective, many more patients would be screened, and probably at an earlier age, than are currently being screened by mammogram today, whether it be by patient preference or by standard of care.
In an article in Nature, Early detection: a long road ahead, the author aimed to create a cancer screening test that was cost effective and could be conducted in a high-throughput manner on a large number of samples. Of 1005 patients who had been recently diagnosed with one of eight types of non-metastatic cancer, the test was able to identify the presence of a tumor (sensitivity) in 33–98% of cases; by contrast, only 7 of 812 (less than 1%) of healthy controls had a positive test.
At the recent American Association for Cancer Research Annual Meeting, AACR annual meeting 2018, data from another cell free DNA broad spectrum test showed sensitivities from 50-95%, depending on the assay or cancer stage.
Both tests report specificities >99%. Although high specificity is important to ensure low numbers of false positives, in an unscreened general population, where disease prevalence is low, this will still result in a substantial number of false positives.
To sum it up, Peter Beitsch, MD, TME - Breast Care Network, Dallas, TX stated, “Blood based screening is just about ready for prime time. It solves many problems of screening tests - mammography (pain, radiation) and colonoscopy (bowel prep, low but real complications) for two examples. More importantly it will now be feasible to ‘screen’ for difficult to detect cancers such as pancreatic cancer (which has no screening guidelines). Lastly, blood based screening will simplify management of patients with germline genetic mutations allowing early detection of associated cancers. So get ready for another revolution in medicine - circulating cell free DNA screening.”
Initially, it seems likely that blood-based screening tests will be most useful in populations already identified as being high risk (for example, smokers or those carrying germline mutations that increase cancer risk), where disease prevalence is higher.
However, these tests appear to be even more promising in the near term as a way to "monitor" patients, both for response to treatment and in follow-up for recurrence. According to Pat Whitworth MD, TME-Breast Care Network, Nashville, TN" These advances hold great promise for both screening and disease monitoring (for response or recurrence). For screening, sensitivity is more important than specificity. Parameters that trigger further investigation can be adjusted to obtain higher sensitivity with less specificity, as is the case with mammography at present. Currently a BIRADS 3 lesion on mammography has about 98% negative-predictive-value, but only about one in five BIRADS 4 lesions turn out to be cancer. When these tests break those thresholds women will prefer a blood test to a mammogram to decide whether further investigation (imaging/biopsy) is needed".