When should PSA be rechecked in a 79‑year‑old man with Gleason 8 prostate cancer post external‑beam radiation therapy who is on continuous androgen‑deprivation therapy, last injection three months ago and PSA <0.1 ng/mL?

PSA Monitoring After External Beam Radiation and ADT

For a 79-year-old man with Gleason 8 prostate cancer who completed external beam radiation and is on continuous ADT with PSA <0.1 ng/mL three months ago, repeat PSA testing should be performed every 3-4 months for the first 2 years, then every 6 months thereafter. 1, 2

Rationale for Monitoring Frequency

The National Comprehensive Cancer Network recommends PSA surveillance every 6-12 months for the first 5 years post-radiation, then annually thereafter. 2 However, given this patient's specific circumstances—high-grade disease (Gleason 8), ongoing ADT, and recent treatment completion—more frequent monitoring is warranted initially. 1

Key Considerations for This Patient

• PSA kinetics after radiation differ fundamentally from post-prostatectomy: PSA gradually declines to a nadir over 18-36 months following radiation completion, rather than becoming undetectable. 1, 2

• ADT suppresses PSA independently: The patient's current PSA <0.1 ng/mL reflects both radiation effect and ongoing androgen suppression. 1 Testosterone recovery after ADT is highly variable and affects PSA kinetics, potentially masking true disease status. 1

• Gleason 8 is the strongest predictor of outcomes: Biopsy Gleason score 8-10 is the most significant predictor of biochemical relapse-free survival, distant metastases-free survival, and prostate cancer-specific mortality after high-dose radiation with ADT. 3

Monitoring Schedule Algorithm

First 2 years post-radiation:

• PSA every 3-4 months 1
• Digital rectal examination annually 2

Years 2-5:

• PSA every 6 months 2
• Digital rectal examination annually 2

Beyond 5 years:

• PSA annually 2
• Digital rectal examination annually 2

What Constitutes Treatment Failure

Biochemical recurrence is defined by the Phoenix criteria: PSA rise ≥2 ng/mL above the nadir PSA. 4, 2 This patient has not yet reached his nadir, which typically occurs 18-30 months after completing radiation. 2

Critical Features Requiring Immediate Action

Do NOT wait for routine follow-up if any of these occur:

• Three consecutive PSA rises (indicates true biochemical progression, not benign "bounce") 4, 1
• PSA doubling time <6 months 1
• Development of bone pain or other symptoms 1
• PSA >10 ng/mL 1

Common Pitfalls to Avoid

Do not order conventional imaging at low PSA levels: Bone scans and CT have extremely low yield when PSA <1.0 ng/mL, with bone scan probability of detecting metastases <5% unless PSA reaches 40-45 ng/mL. 2 If imaging is needed, PSMA PET/CT is far superior for detecting occult disease. 4

Do not reflexively start salvage therapy based on single detectable PSA: Transient PSA rises ("bounces") occur in 12-61% of patients after radiation and resolve spontaneously without intervention. 1 Three consecutive rises are required to distinguish true progression from benign fluctuations. 4, 1

Do not ignore the possibility of PSA-independent progression: In high-grade disease (Gleason ≥8), particularly with atypical histologic variants, progression can occur with undetectable or low PSA levels. 5 Eighty-five percent of such patients had Gleason scores ≥7, and 46% had atypical histologic variants. 5

Prognostic Context

This patient's Gleason 8 disease places him in the unfavorable high-risk category. 3 At 10 years after high-dose radiation with ADT, patients with Gleason 8-10 have a prostate cancer-specific mortality rate of 14.4% and distant metastases-free survival of 71.6%. 3

However, achieving a PSA nadir <0.06 ng/mL is a strong independent predictor of excellent outcomes. 6 If this patient reaches such a nadir, his prognosis improves substantially, and ADT duration of 12 months may be sufficient. 6 Conversely, failure to reach nadir <0.06 ng/mL suggests need for 18 months total ADT duration. 6