Expected PSA Trend After External Beam Radiation for Gleason 6 Prostate Cancer
Following external beam radiation therapy for Gleason 6 prostate cancer, PSA should decline to ≤1.0 ng/mL within 16 months and ideally reach a nadir of ≤0.5 ng/mL within 18–30 months, with the current PSA of 2.9 ng/mL expected to continue trending downward over the next 1–2 years. 1
Expected PSA Kinetics After Radiation
PSA decline after external beam radiation is gradual and continues for 18–30 months post-treatment, unlike the immediate undetectable levels expected after radical prostatectomy. 1
The PSA nadir (lowest point) typically occurs at a median of 18–24 months after completing radiation therapy, though it may take up to 30 months in some patients. 2, 3
A PSA nadir of ≤0.5 ng/mL is associated with the highest probability of long-term biochemical control, with 95% 5-year disease-free survival and 84% 10-year disease-free survival. 3
Patients achieving a nadir of 0.5–0.9 ng/mL have approximately 60% 5-year biochemical control, while those with nadir 1.0–1.9 ng/mL have 50% control. 2
Prognostic Indicators for This Patient
For low-risk disease (Gleason 6, PSA initially low), the time to reach nadir is typically longer—often 2–3 years—compared to higher-risk disease. 2
Patients who take ≥2.0 years to reach a nadir of ≤0.4 ng/mL have the highest probability of cure, with 100% biochemical control in one series. 2
The current PSA of 2.9 ng/mL is within the expected range during the first 1–2 years post-radiation and should continue declining if treatment is successful. 1, 2
Surveillance Protocol
PSA should be measured every 6–12 months for the first 5 years, then annually thereafter. 1
Digital rectal examination should be performed annually, though it may be omitted if PSA remains stable and low. 1
The first follow-up visit should occur at 3 months post-treatment to establish baseline, then continue with regular monitoring. 1
Definition of Biochemical Failure
Biochemical recurrence after radiation is defined by the Phoenix Consensus criteria: a rise of ≥2.0 ng/mL above the PSA nadir. 1
Failure is determined "at call" (not backdated to the first PSA rise), meaning the date of failure is when the 2 ng/mL rise above nadir is documented. 1
Biochemical failure rarely occurs beyond 5 years post-treatment; only 6 of 136 at-risk patients failed after 5 years in one large series. 2
Common Pitfalls to Avoid
Do not interpret transient PSA rises ("benign bounces") as treatment failure—these are common after brachytherapy and can occur with external beam radiation. 1
Do not initiate salvage therapy based on a single elevated PSA; confirm the trend with serial measurements showing consistent rise of ≥2 ng/mL above nadir. 1
Patients with lower pretreatment PSA and Gleason scores require longer follow-up (often 3–5 years) to achieve certainty of cure compared to higher-risk patients. 2
A PSA that remains elevated at 1.5–2.0 years post-treatment does not necessarily indicate failure if it is still declining; continue monitoring for up to 30 months before concluding treatment efficacy. 1, 2
Reassurance for This Patient
The current PSA of 2.9 ng/mL with a downward trend is consistent with successful treatment response, as the nadir has not yet been reached. 1, 2
Continue monitoring PSA every 6 months; expect further decline over the next 12–18 months to a goal nadir of ≤1.0 ng/mL, ideally ≤0.5 ng/mL. 1, 3
If PSA reaches ≤0.5 ng/mL and takes ≥2 years to reach this level, the probability of long-term biochemical cure approaches 100%. 2