A large review of 35 studies involving nearly 7,000 women looked at whether certain substances in the blood could help detect breast cancer early. The substances studied were tiny molecules called microRNAs and other fats and chemicals (lipidomic/metabolomic biomarkers) that can be measured in a blood sample. The goal was to see how well these blood tests could tell apart women who had breast cancer from those who did not.
The results showed that these blood markers performed very well overall. On average, the tests correctly identified 87 out of every 100 women who had breast cancer (sensitivity). They also correctly ruled out breast cancer in 84 out of every 100 women who did not have the disease (specificity). The overall diagnostic accuracy, measured by the area under the curve (AUC), was 0.92, which is considered excellent.
However, the review also found important limitations. There was a lot of variation among the studies, meaning the results were not consistent. For example, the sensitivity varied widely from one study to another. This inconsistency is measured by something called I-squared, which was very high (88% for sensitivity and 90% for specificity). This suggests that the accuracy of these blood tests might depend on many factors, such as the type of breast cancer, the specific markers measured, or the population studied.
Another concern is that most of the studies were done in a way that can overestimate the accuracy of a test. They used a design called retrospective case-control, where researchers look back at stored blood samples from women already known to have cancer or not. This can make a test look better than it would in a real-world screening setting, where the goal is to find cancer in women who have no symptoms.
Because of these limitations, the researchers caution that these blood tests are not ready to replace mammograms for breast cancer screening. They are best seen as investigational tools that might one day be used alongside mammography, especially for women who cannot easily get mammograms or who need additional testing. More research is needed, especially studies that follow women over time (prospective studies) to see how well these tests work in real-world screening programs.
In summary, blood-based biomarkers show promise for detecting breast cancer early, but they are not yet reliable enough for widespread use. The high accuracy seen in studies is encouraging, but the inconsistency and study design issues mean that more work is needed before these tests can be recommended for routine screening.
