Using PSA to Monitor Prostate Cancer Progression

Editor's note: second of two parts; read part one here.

In the first part of our series, we described how PSA is used as a screening tool to help detect prostate cancer in men without symptoms. While PSA screening can save lives, it often identifies slow-growing cancers that may never become deadly and can rise for reasons unrelated to cancer, such as prostate inflammation or benign enlargement. These factors have raised concerns about unnecessary tests and overdiagnosis.

Active Surveillance

Doctors measure PSA to monitor disease progression in men on active surveillance for low-risk prostate cancer. A rising PSA level may indicate the need for treatment.

Post-Prostatectomy Monitoring

After surgical removal of the prostate, PSA should be undetectable, since all PSA-producing cells are removed. A subsequent rise in PSA indicates biochemical recurrence, meaning residual cancer cells remain in the body.

Post-Radiation Monitoring

Radiation destroys cancer cells in the prostate but leaves healthy gland tissue intact. PSA levels drop to a nadir—the lowest post-treatment level—ideally below 0.5 ng/mL. Biochemical recurrence is diagnosed if PSA rises by at least 2 ng/mL above the nadir.

Imaging and Nonmetastatic Prostate Cancer

Traditionally, doctors use bone scans and CT of the abdomen and pelvis to detect metastases. If these scans are negative despite rising PSA, the condition is called nonmetastatic prostate cancer. PSA doubling time—rapid doubling within six to eight months—can prompt further intervention, while slower doubling may allow continued observation.

PSMA PET Scans

A newer imaging technique uses a tracer that binds to prostate-specific membrane antigen (PSMA) on cancer cells, allowing detection of tiny metastases undetectable by traditional methods.

Monitoring Metastatic Disease Treatment

In men with metastatic prostate cancer, PSA is checked every three months to assess treatment efficacy. Falling or stable PSA levels indicate effective therapy. Modern treatments may be paused indefinitely if PSA remains undetectable and metastases are no longer visible.

Evaluating Experimental Therapies

For advanced prostate cancer, experimental therapies are assessed by PSA response. A drop of 50% or more in PSA is considered a positive treatment indicator.

"PSA monitoring continues to be one of the most important evaluations that physicians and clinicians can perform to determine the best treatments for men with prostate cancer," says Dr. Marc B. Garnick.