Researchers seek better test for PSA

DEAR DOCTOR K: I keep hearing about problems with the PSA test. Are any new screening tests for prostate cancer in development?

DEAR READER: Prostate-specific antigen (PSA) is a biomarker. Biomarkers are chemicals that can reveal that something abnormal is happening in the body. PSA is a chemical released by cells in the prostate gland. It is released at relatively high levels when prostate cells turn cancerous. However, PSA also is released in noncancerous prostate conditions.

However, there are two problems with the test. First, as just mentioned, high PSA levels do not always indicate that there is prostate cancer.

Second, the PSA levels measured by the test can sometimes be normal even when a person does have prostate cancer.

The third problem with the test is that even when it accurately detects prostate cancer, it doesn’t distinguish aggressive cancer from nonaggressive cancer. If the PSA test detects a prostate cancer that will not grow and spread, then detecting it can lead to invasive diagnostic tests that can have harmful side effects of their own, and to overtreatment of a cancer that will never cause any harm. The diagnosis and treatment will be worse than the disease.

Scientists are looking for biomarkers that have fewer falsely positive and falsely negative results, and that distinguish between aggressive and nonaggressive prostate cancers. Here are two of the most promising options:

• GENETIC TESTS OF PROSTATE TISSUE. Cells in the prostate gland turn cancerous because of changes in their genes. Certain changes in genes lead to aggressive cancers. These genetic changes can be identified in biopsy specimens of the cancer.

• CIRCULATING TUMOR CELLS. Cancer spreads when tumor cells break away, get swept up into the bloodstream and start to grow in other parts of the body. A new “liquid biopsy” uses a simple blood test to measure circulating tumor cells and their telltale markers, which could someday reduce the need for follow-up biopsies.