Doctors often use a blood test called prostate-specific antigen, or PSA, to follow prostate cancer.
When treatment works, PSA usually falls, but doctors still need clear targets that show whether a patient is responding well enough.
A large real-world study has now found that one very low PSA level may be especially meaningful for men with prostate cancer that has spread beyond the prostate. Patients whose PSA fell below 0.2 nanograms per milliliter within nine months of starting treatment had substantially better survival.
The research was published online in CANCER, a peer-reviewed journal of the American Cancer Society. The study used health records from the U.S. Veterans Health Administration and included 4,890 patients treated between 2018 and 2023.
These patients had metastatic hormone-sensitive prostate cancer. This means the cancer had already spread to other parts of the body but was still responding to treatments that lower or block testosterone.
Testosterone can help many prostate cancers grow. For that reason, a standard treatment is androgen deprivation therapy, which greatly reduces the body’s supply of male hormones or blocks their effects on cancer cells.
Doctors often combine this treatment with another medicine to improve cancer control. Even with modern treatments, however, patients can respond very differently, making early signs of treatment success extremely useful.
PSA is a protein made by prostate cells, including prostate cancer cells. A falling PSA level after treatment generally suggests that cancer activity is decreasing, but researchers have debated which type of PSA response gives the clearest information about a patient’s future.
Earlier phase 3 clinical trials suggested that reaching a PSA level below 0.2 ng/mL was strongly linked with better outcomes. In everyday medical practice, however, doctors may also look at the percentage by which PSA falls, such as whether it drops by 90%.
The new study tested these measures in a large group of patients receiving care outside a clinical trial. Researchers followed the veterans for a median of about two years, and 896 patients died during that period.
The strongest signal came from the actual PSA level reached. Men whose PSA fell below 0.2 ng/mL within nine months were 54% less likely to die than men whose PSA never reached that low level.
Importantly, the size of the percentage decline did not add the same value. Patients whose PSA fell by at least 90% but remained above 0.2 ng/mL did not show an improvement in survival.
This suggests that a dramatic drop is not necessarily enough if the final PSA level remains relatively high. In practical terms, the destination may matter more than how far the PSA traveled to get there.
The study also found that patients receiving testosterone-lowering treatment together with another drug that further blocks testosterone were more likely to reach the very low PSA target. This supports the growing use of stronger combination treatment for suitable patients with metastatic disease.
Dr. Stephen J. Freedland, professor of urology at Cedars-Sinai and a staff physician at the Durham VA Medical Center, said the findings support using PSA below 0.2 ng/mL as a treatment goal. Patients who fail to reach that target may need closer attention or consideration of stronger treatment.
The study has important strengths because it examined thousands of patients receiving routine care. Real-world research can show whether results seen in tightly controlled clinical trials also appear in everyday medical settings.
Still, the findings should not be treated as proof that forcing PSA below 0.2 ng/mL will automatically make every patient live longer. This was an observational analysis, and people who achieve very low PSA may have cancers that are naturally more sensitive to treatment.
The results are best viewed as evidence that PSA below 0.2 ng/mL is a powerful marker of treatment response and prognosis. Future studies should test whether changing treatment early in patients who miss this target can actually improve survival.
For patients and doctors, the study offers a simple and potentially useful benchmark. A very low PSA within the first nine months may identify people doing especially well, while failure to reach that level could signal a need to reassess the treatment plan.
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Source: Cedars-Sinai.
