A cancer detection blood test is the holy grail of cancer detection. Today, if you are doing everything you can to prevent dying of cancer, you need to get, at appropriate ages, colonoscopy, pap smear and mammograms if you are a woman, and CAT scans of the chest if you are a present or former smoker. These tests are inconvenient, expensive, and, in the case of colonoscopy, unpleasant. Wouldn’t it be great if you could get a single blood test instead? In The Lancet Oncology published in June, 2023 is a provocative article from Oxford University. Study subjects were over eighteen and had to have non-specific symptoms possibly caused by cancer. 5461 pe0ple were identified and had a blood test looking for tumor-related mutated DNA in the blood stream. These people were then evaluated by traditional means — history, physical examination, blood tests and x-rays. 6.7% of these people were found to have cancer. 75% of the people with a positive blood test for cancer actually had it. 97% of the people with a negative blood test did not have cancer. The sensitivity of the test (to find cancer) was 66%. The specificity (a positive blood test actually means cancer) was 98%. Sensitivity and specificity increased with age. The largest single diagnosis was lung cancer. How does this compare with traditional tests? Very well. By comparison, only 50% of women with a positive mammogram will turn out to have cancer. 10% of people with colon cancer had a negative colonoscopy within the last ten years.
What role will this blood test play in coming years, especially as the blood test gets better? Ideally all of the other tests will go away, except in patients with positive blood tests. Stay tuned. For a copy of this article, send Dr. Stark a request (use the form to the right of this page).