When prostate cancer spreads to distant parts of the body, doctors need fast and reliable ways to judge whether treatment is controlling it.
A new study suggests that one simple number from a routine blood test may provide an especially useful clue.
The number is 0.2 ng/mL. Researchers found that men with metastatic prostate cancer who brought their PSA below this level during the first nine months of treatment were much more likely to survive than those who did not.
The findings were published online in CANCER, the journal of the American Cancer Society. Researchers examined records from 4,890 patients in the U.S. Veterans Health Administration who were treated for metastatic hormone-sensitive prostate cancer from 2018 through 2023.
Prostate-specific antigen, better known as PSA, is produced by cells in the prostate. Doctors commonly measure it in blood to help detect prostate problems and to monitor people who have already been diagnosed with prostate cancer.
After cancer treatment begins, PSA can act like a rough signal of how active the disease remains. If cancer cells are being controlled, the amount of PSA in the blood often falls.
But there are several ways to describe a successful fall. One patient might have a 90% drop but still have a measurable PSA level, while another might reach an extremely low level below 0.2 ng/mL.
That distinction was at the heart of the new research. The investigators wanted to know which measure was more closely connected with survival in patients treated in ordinary healthcare settings rather than only in clinical trials.
All patients had cancer that had spread but was still sensitive to hormone treatment. Most prostate cancers depend partly on testosterone, so treatment commonly includes medicines or procedures that sharply reduce testosterone activity.
Some patients also receive additional drugs that block the cancer’s access to male hormones more completely. Modern treatment increasingly uses these combinations because metastatic prostate cancer can eventually learn to grow even when testosterone levels are very low.
During a median follow-up of roughly two years, 896 of the patients died. The researchers compared survival with PSA results recorded during the first nine months after treatment began.
Patients who reached PSA below 0.2 ng/mL had a 54% lower risk of death than patients who did not reach that level. This association remained whether or not their PSA had also fallen by at least 90%.
The reverse result was particularly revealing. A decline of 90% or more did not predict better survival when the patient’s PSA still remained at or above 0.2 ng/mL.
Imagine two men starting treatment with very different PSA levels. A 90% reduction may sound impressive for both, but if one man’s PSA remains clearly detectable while the other’s falls to an extremely low level, their outlook may not be the same.
The researchers also found that patients treated with hormone suppression plus an additional testosterone-blocking medicine were more likely to reach the low PSA target. That observation fits with evidence that stronger treatment combinations can produce deeper cancer responses.
Corresponding author Dr. Stephen J. Freedland of Cedars-Sinai and the Durham VA Medical Center said PSA below 0.2 ng/mL should be considered an important measure of treatment success. The results may also help doctors recognize patients whose disease is not responding deeply enough.
That does not mean a patient whose PSA remains above 0.2 ng/mL has run out of options. Instead, the result could become a warning signal that encourages doctors to review treatment, check other signs of disease and consider whether therapy should be intensified.
There are limits to what the study can tell us. It looked back at medical records rather than randomly assigning patients to different treatment decisions based on their PSA, so it cannot prove that changing therapy at the nine-month mark will improve survival.
The population was also drawn from the Veterans Health Administration, which may differ from the broader population of people with prostate cancer. Further studies will be needed to see how well the target performs across more diverse groups and treatment settings.
Even with those cautions, the study strengthens evidence from earlier phase 3 trials and gives doctors a clear number that is easy to measure. The most important next question is whether acting on this marker can help patients who do not reach it live longer.
For now, the findings make PSA below 0.2 ng/mL a promising sign of a deep treatment response. A tiny number on a blood test may therefore carry valuable information about how well advanced prostate cancer is being controlled.
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Source: Cedars-Sinai.
