In a 64-year-old man with de novo low-volume metastatic hormone-sensitive prostate cancer receiving continuous androgen deprivation therapy (ADT) plus enzalutamide, who has undetectable PSA after 20 months but significant fatigue, hot flashes, decreased libido, and cognitive slowing, what does the current evidence indicate regarding intermittent versus continuous therapy?

Option C is the most accurate statement regarding intermittent versus continuous therapy in this clinical scenario.

SWOG 9346 failed to demonstrate non-inferiority of intermittent ADT in metastatic hormone-sensitive prostate cancer, showing a trend toward worse survival (5.1 vs 5.8 years, HR 1.10,95% CI 0.99-1.23). 1 This is critical because your patient has metastatic disease, and the only adequately powered trial designed to assess non-inferiority in this population did not meet its primary endpoint. The upper confidence interval exceeded the prespecified non-inferiority margin of 1.20, meaning a 20% greater mortality risk with intermittent therapy cannot be ruled out 2.

Key Evidence Distinguishing the Options

Why Option A is Incorrect

SWOG 9346 explicitly did not establish non-inferiority of intermittent ADT in mHSPC 1. The St. Gallen consensus (2015) stated that "the value of iADT in men with metastatic castration-naïve prostate cancer is still controversial since the only study powered and designed to assess non-inferiority, the SWOG 9346 trial, failed to show non-inferiority" 1. Only 71% of panelists recommended intermittent ADT for a minority of selected metastatic patients 1.

Why Option B is Incomplete

While A-DREAM data exists regarding treatment interruption after ADT plus androgen receptor pathway inhibitors (ARPIs), Option B focuses only on the negative aspect (rare testosterone recovery) without acknowledging the more nuanced findings about treatment-free status maintenance in favorable responders.

Why Option D is Wrong

A-DREAM did not show equivalent outcomes regardless of disease volume. In fact, SWOG 9346 post-hoc analysis suggested differential effects by disease burden: patients with minimal disease had median survival of 5.4 years with intermittent ADT versus 6.9 years with continuous ADT (HR 1.19), while extensive disease showed 4.9 vs 4.4 years (HR 1.02) 2. This indicates disease volume should factor into decision-making.

Clinical Application to Your Patient

Your patient presents a complex scenario:

• De novo low-volume mHSPC (3 bone lesions)
• Deep PSA response (undetectable <0.1 ng/mL) after 20 months
• ADT + enzalutamide (not traditional ADT alone)
• Significant quality-of-life impairment

Critical Considerations

The evidence gap: All major trials of intermittent therapy (SWOG 9346, PR.7) studied ADT alone, not ADT plus novel hormonal agents like enzalutamide 1, 2, 3. The 2021 ASCO guideline explicitly states: "IADT has not been studied in combination with additional cytotoxic or hormonal agents in this population" 3.

FDA labeling guidance: The enzalutamide label does permit treatment suspension in nmCSPC with high-risk biochemical recurrence if PSA becomes undetectable (<0.2 ng/mL) after 36 weeks, with reinitiation at PSA ≥2.0 ng/mL (post-prostatectomy) or ≥5.0 ng/mL (post-radiation) 4. However, this applies to non-metastatic disease, not your patient's metastatic presentation.

Testosterone recovery challenge: Even if treatment is interrupted, testosterone recovery within 18 months is rare with ADT plus ARPI combinations, potentially limiting the quality-of-life benefits that motivated the treatment break [@Option C context from A-DREAM].

Recommendation Framework

A treatment holiday discussion is reasonable but must be framed as investigational given:

1. Favorable factors supporting discussion:

   • Low-volume disease at presentation
   • Deep PSA response (undetectable)
   • Prolonged response duration (20 months)
   • Significant treatment-related toxicity affecting quality of life
   • Patient preference and autonomy

2. Unfavorable factors requiring caution:

   • Metastatic disease (not biochemical recurrence alone)
   • SWOG 9346 failed to show non-inferiority in mHSPC
   • No randomized data for interruption of ADT + enzalutamide in metastatic disease
   • Uncertain testosterone recovery with combination therapy
   • Risk of disease progression during off-treatment period

3. Monitoring requirements if proceeding:

   • PSA every 4-8 weeks initially
   • Testosterone levels to assess recovery
   • Imaging at PSA progression or clinical symptoms
   • Predefined PSA threshold for treatment reinitiation (e.g., 2-5 ng/mL)
   • Close surveillance for symptomatic progression

The patient should understand this represents extrapolation from biochemical recurrence data and FDA labeling for non-metastatic disease, with ongoing randomized trials needed to definitively answer this question in the metastatic setting [@11