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A man’s prostate-specific antigen (PSA) blood level is often a good indicator of how effective treatment has been.

PSA level as a tool to monitor prostate cancer

Generally speaking, your PSA level should get very low after treatment. But PSA results only give a limited amount of information, and sometimes doctors aren’t sure what they mean.

Before starting treatment, you might want to ask your doctor what your PSA level is expected to be during and after treatment, and what levels might cause concern. It’s important to know that the PSA level is only one part of the overall picture. Other factors can also play a role in determining if cancer is still there, if it is growing, or if it has come back.

It’s also important to know that PSA levels can sometimes fluctuate a bit on their own, even during or after treatment, so they may not always be an accurate sign of what is happening with your cancer. Understandably, many men being treated for prostate cancer are very concerned about even small changes in their PSA levels. The PSA level is an important tool to monitor the cancer, but not every rise in PSA means that the cancer is growing and requires treatment right away.

During active surveillance or watchful waiting (observation)

If you choose active surveillance or observation, your PSA level will be monitored closely (most likely along with other tests) to help decide if the cancer is growing and if treatment should be considered.

Not all doctors agree on exactly what PSA level might require further action (such as a prostate biopsy or treatment), whether it’s a set number or how quickly it’s rising. Again, talk to your doctor so you understand what change in your PSA might be considered cause for concern.

After surgery (prostatectomy)

Your PSA should fall to a very low or even undetectable level within a couple of months after radical prostatectomy. Because some PSA can remain in the blood for several weeks after surgery, even if all of the prostate cells were removed, doctors often advise waiting at least 6 to 8 weeks after surgery before checking the PSA level.

Some men might worry if their PSA is still detectable even at a very low level after surgery, but this does not always mean cancer is still in the body. Modern PSA blood tests can detect even tiny amounts of PSA, but these amounts might not always be significant, especially if they are not rising over time. It could just mean that you have some cells in the body making PSA, but these aren’t necessarily cancer cells.

Still, having any detectable PSA after surgery can be stressful for men and their loved ones. If your PSA is still detectable after surgery, even at a very low level, talk to your doctor about what it might mean, and what the best course of action might be. Some doctors advise following such low PSA levels over time to get a better idea of what’s going on. Other doctors might recommend further treatment.

If your PSA increases after surgery, your doctor might also want to know how fast it is rising. Some evidence shows that faster-rising PSA levels may be more of a concern. Men who have a shorter PSA doubling time (the time it takes for the PSA level to double) tend to have a worse prognosis (outlook) compared to men with longer PSA doubling times.

After radiation therapy

Radiation therapy doesn’t kill all of the cells in the prostate gland, so it's not expected to cause the PSA to drop to an undetectable level. The remaining normal prostate cells will still make some PSA.

The pattern of the drop in PSA after radiation therapy is also different from after surgery. PSA levels after radiation tend to drop slowly, and they might not reach their lowest level until 2 years or more after treatment.

Doctors tend to follow the PSA levels every few months to look for trends. A one-time, small rise in PSA might be cause for closer monitoring, but it might not mean that the cancer is still there (or has returned), as PSA levels can fluctuate slightly from time to time. However, a PSA that is rising on consecutive tests after treatment might indicate that cancer is still there. Some medical groups have proposed that if the PSA rises more than 2 ng/mL above the lowest level reached, further treatment should be considered, but some doctors might advise tests to look for cancer in the body even if the PSA has not yet risen this much.

As is the case after surgery, if your PSA begins to rise after radiation treatment, your doctor might also want to know how fast it is rising. Men who have a shorter PSA doubling time (the time it takes for the PSA level to double) tend to have a worse prognosis (outlook) compared to men with longer PSA doubling times.

There is also a phenomenon called a PSA bounce that sometimes happens after external beam radiation and brachytherapy. The PSA rises slightly for a short time within the first couple of years after treatment, but then goes back down. Doctors aren’t sure why this happens, but it doesn’t seem to affect a man’s prognosis.

During treatment for advanced prostate cancer

When treatments such as hormone therapy, chemotherapy, or immunotherapy are used for more advanced prostate cancer, the PSA level can help show how well the treatment is working or when it might be time to try a different treatment.

Treatments should lower the PSA level (at least at first), although in some cases they may just help keep it from rising further, or even just slow the rise. Of course, other factors, such as whether you’re having symptoms from your cancer and whether imaging tests show it is growing, are also important when deciding if it might be time to change treatments.

If the cancer has spread outside the prostate, the actual PSA level is often not as important as the direction and speed with which it changes. The PSA level itself does not predict whether or not a man will have symptoms or how long he will live. Many men have very high PSA levels and feel just fine, while other men with low PSA levels might have symptoms.