Tumor marker tests are typically done when cancer is or has been known to be present in a patient and are therefore not a routine aspect of medical practice. Cancer markers are not considered an effective tool for routine preventative screening, according to the National Cancer Institute.
Tumor markers are useful in determining whether or not cancer is responding to treatment or if a tumor has recurred. No tumor marker that has been discovered as of August of 2015 has been sensitive or specific enough to indicate the presence of cancer for preventative screening purposes. To illustrate this point, the Prostate Specific Antigen, or PSA, blood test has been used as a screen for prostate cancer, but randomized controlled trials have shown that heightened levels of PSA are not a good indicator that a patient has prostate cancer, says the National Cancer Institute. There are many benign conditions that can also result in heightened levels of PSA.
For a screening test to be useful, it must be highly sensitive and highly specific to the disease for which it is being screened. If a test is highly sensitive, it does not result in a high number of false negatives, and if a test is highly specific, it does not result in a large number of false positives, according to the National Cancer Institute.