What is the recommended timing for repeat scans in a patient with metastatic prostate cancer on Lupron (leuprolide), Xtandi (enzalutamide), and Zometa (zoledronic acid) with stable disease and a PSA level of <0.04?

Monitoring Schedule for Metastatic Prostate Cancer with Stable Disease

For a patient with metastatic prostate cancer on Lupron, Xtandi, and Zometa with stable disease (non-PSMA avid sclerotic bone lesions) and undetectable PSA (<0.04), repeat imaging should be performed every 6 months in the absence of new symptoms or PSA elevation.

Monitoring Approach for Patients on Enzalutamide (Xtandi)

The monitoring schedule for patients with metastatic prostate cancer on androgen deprivation therapy (ADT) with enzalutamide should follow a structured approach:

PSA Monitoring

• PSA should be measured every 2-4 months 1
• Continue monitoring despite current undetectable levels (<0.04 ng/mL)
• More frequent testing (every 3-4 weeks) may be considered if clinical concerns arise

Imaging Schedule

• CT scans: Every 6 months in the absence of symptoms 1
  • 59% of experts recommend bone scans every 6 months
  • 31% recommend CT scans every 6 months
• PSMA PET/CT: Consider repeating annually if previously used for staging, especially with non-avid lesions requiring monitoring

Clinical Assessment

• Physical examination with digital rectal exam every 3-6 months 1
• Monitor for new symptoms that might warrant earlier imaging:
  • New bone pain
  • Neurological symptoms
  • Unexplained weight loss
  • Change in performance status

Special Considerations for This Patient

Stable Disease Indicators

• Current PSA <0.04 ng/mL (excellent response)
• Non-PSMA avid sclerotic bone lesions on recent imaging
• Stable findings on CT CAP

Risk-Adapted Approach

The St. Gallen Advanced Prostate Cancer Consensus Conference recommends a risk-adapted approach to imaging frequency based on:

• Response to therapy (currently excellent)
• Extent of disease (stable bone metastases)
• Clinical situation (currently stable) 1

When to Consider Earlier Imaging

Repeat imaging should be performed earlier than the scheduled 6-month interval if:

1. PSA rises above 0.2 ng/mL on two consecutive measurements
2. New symptoms develop (particularly bone pain)
3. Abnormal findings on physical examination
4. Deterioration in performance status

Interpretation of Imaging Results

Bone Lesions

• Sclerotic bone lesions that are not PSMA-avid may represent treated/healing metastases
• Stable appearance on conventional imaging is reassuring
• Lack of PSMA avidity may indicate treatment response

PSA Correlation

• Continue to correlate imaging findings with PSA trends
• Be aware that PSA may not always correlate with imaging findings, particularly with bone metastases

Common Pitfalls to Avoid

1. Overreliance on PSA alone: While PSA is valuable, some progression can occur with stable PSA values, particularly in patients on enzalutamide
2. Unnecessary frequent imaging: In stable patients with undetectable PSA, frequent imaging adds cost without clinical benefit
3. Misinterpreting sclerotic lesions: Sclerotic bone lesions may represent healing metastases rather than active disease
4. Ignoring clinical symptoms: New symptoms should prompt earlier imaging regardless of PSA values

The current excellent response to therapy (undetectable PSA, stable imaging findings) supports a monitoring approach with imaging every 6 months, which balances the need for surveillance with avoiding excessive testing.