From the Guidelines
After radiation therapy for localized prostate cancer, PSA levels typically decrease gradually but usually do not become undetectable, with a goal of reaching a PSA nadir of less than 0.5 ng/mL, as stated in the 2009 update by the Journal of Urology 1. This is because some healthy prostate tissue remains after radiation therapy and continues to produce small amounts of PSA, making it normal and expected to have a low but still measurable PSA level. The change in PSA following interstitial prostate brachytherapy is complex and is characterized by intermittent rises called “benign bounces,” with a median PSA level of 0.1 ng/ml, as noted in the study published in the Journal of Urology 1. Physicians monitor PSA trends over time rather than focusing on a single value, looking for stability at a low level, and a consistent rise in PSA after reaching nadir (known as biochemical recurrence) would be concerning and warrant further evaluation, as suggested by the eligibility and outcomes reporting guidelines for clinical trials for patients in the state of a rising prostate-specific antigen 2. Some key points to consider include:
- The American Society for Therapeutic Radiation Oncology (ASTRO) has developed a consensus definition for biochemical failure after radiotherapy as three consecutive rises in PSA starting at least 2 years after the start of radiation, with the time of failure as the midpoint between the nadir and the first confirmed rise.
- The minimum PSA level to consider a patient eligible for clinical trials in this state was arbitrarily defined as a value ≥ 0.4 ng/mL at a minimum of 1 month after surgery, which is confirmed on a subsequent test followed by a value equal to or greater than the previous value, as discussed in the Journal of Clinical Oncology 2. Regular PSA monitoring typically occurs every 3-6 months initially, then annually if levels remain stable, and patients should understand that some fluctuation in PSA levels is normal after radiation therapy and doesn't necessarily indicate cancer recurrence. It's also important to note that the PSA level should fall to a low level and then remain stable after radiation therapy, and a consistently rising PSA level usually, though not always, indicates cancer recurrence, as stated in the study published in the Journal of Urology 1.
From the Research
Prostate-Specific Antigen (PSA) Levels After Radiation Therapy
- PSA levels typically decrease significantly after radiation therapy for localized prostate cancer, as shown in a study from 1991 3.
- In this study, PSA values fell dramatically in virtually all patients (98%) by 3 months follow-up, with a mean PSA decrease from 12.5 to 2.6 ng/ml.
- However, PSA was still detectable in the serum of all patients, indicating that it is not typically undetectable after radiation therapy.
Factors Influencing PSA Levels After Radiation Therapy
- A study from 2024 found that patients with a PSA nadir >0.01 ng/mL had a significantly higher biochemical failure rate and clinical failure rate 4.
- Another study from 2017 found that the use of radiation therapy was the most powerful predictor of both cause-specific and overall survival, even in patients with extremely high PSA levels (≥25 ng/mL) 5.
- A study from 2020 found that salvage radiation therapy prolonged the time to treatment failure of bicalutamide in patients with post-radical prostatectomy PSA failure 6.
PSA Bounce After Radiation Therapy
- A systematic review and meta-analysis from 2021 found that PSA bounce after definitive radiation therapy was associated with better biochemical recurrence-free survival 7.
- This study suggested that PSA bounce may be a positive prognostic factor for patients with localized prostate cancer treated with radiation therapy.