PSA Monitoring After External Beam Radiation for Gleason-6 Prostate Cancer
For a 66-year-old patient with Gleason-6 prostate cancer who received external beam radiation (EBR) in December 2024 and shows declining PSA values (4.0 in April 2025 to 3.2 in August 2025), the next step is continued PSA monitoring every 3-6 months with no immediate intervention needed at this time.
Current Status Assessment
The patient presents with:
- Gleason-6 prostate cancer (low-risk disease)
- Treatment with external beam radiation completed in December 2024
- PSA values showing appropriate decline:
- 4.0 ng/mL (April 2025, ~4 months post-treatment)
- 3.2 ng/mL (August 2025, ~8 months post-treatment)
Interpretation of Current PSA Trend
The patient's PSA values demonstrate a favorable response to radiation therapy:
- The declining PSA pattern (from 4.0 to 3.2 ng/mL) is consistent with an appropriate response to radiation therapy
- PSA typically continues to decline for 18-30 months after radiation therapy before reaching nadir 1
- Unlike radical prostatectomy, PSA values <0.2 ng/mL are uncommon after external beam radiotherapy 1
- The patient is still within the expected PSA decline phase post-radiation
Recommended Monitoring Protocol
Short-term Follow-up
- Continue PSA monitoring every 3-6 months 1
- Include digital rectal examination (DRE) at each follow-up visit
- Next PSA check should be scheduled for November 2025-January 2026
Long-term Follow-up
- After 2 years, if PSA remains stable or continues to decline, transition to annual monitoring 1
- Continue indefinite follow-up to monitor for potential late recurrence
Definition of Biochemical Failure
According to the Phoenix definition (ASTRO/RTOG consensus), biochemical failure after radiation therapy is defined as:
Important Considerations
PSA Bounce Phenomenon
- Approximately 12% of patients experience a transient PSA bounce after radiation therapy 3
- A PSA bounce is defined as an increase of at least 0.5 ng/mL followed by a decrease to pre-bounce levels 3
- Mean time to PSA bounce is around 9 months post-therapy 3
- This phenomenon should not be confused with true recurrence and does not predict biochemical recurrence 3
When Intervention Would Be Warranted
Intervention would only be indicated if:
- PSA rises ≥2.0 ng/mL above the eventual nadir value 2, 1
- Three consecutive PSA rises are documented 2
- Imaging or clinical examination reveals evidence of recurrence
Conclusion
The patient's current PSA trend shows an appropriate response to radiation therapy with no signs of biochemical failure. The declining PSA values from 4.0 to 3.2 ng/mL represent an expected pattern during the first year after radiation treatment. Continue regular PSA monitoring every 3-6 months with DRE at each visit, with no immediate intervention needed at this time.