A decrease in prostate-specific antigen (PSA) levels is seen in some men with advanced prostate cancer who are treated with Xtandi (enzalutamide).

PSA is a protein made by prostate cells. It is mainly found in semen, with only small amounts normally being found in the bloodstream.

Levels of PSA in the blood can become elevated when there is a problem with the prostate, such as when prostate cancer develops. A PSA test, which involves measuring PSA levels in a small amount of blood, can be used to help screen men for prostate cancer.

PSA levels can also be elevated for other reasons, however. Prostatitis, age, benign prostatic hyperplasia, irritations or infections, and other factors can also increase PSA levels, so a single elevated PSA level alone is not used to diagnose prostate cancer. PSA screening is a useful first step to help identify, which men need further testing.

Xtandi and monitoring PSA levels

Xtandi is an androgen receptor inhibitor and works by blocking the action of testosterone at the androgen receptor - reducing how often androgens can connect with the receptor - which helps prevent prostate cancer cells from growing and spreading.

Monitoring PSA levels in the blood is one of the methods used to determine how prostate cancer is responding to treatment with Xtandi. Rising PSA levels during treatment may indicate the treatment is no longer working.

During clinical trials, researchers count the number of men whose PSA levels reduce by 50 percent or more following the initiation of treatment with Xtandi. This is one of the ways in which they assess how well Xtandi is working.