A 72-year-old man with metastatic castration-resistant prostate cancer (mCRPC) who has progressed on leuprolide and bicalutamide combination therapy is now being considered for next-line hormonal therapy. Which agent is the preferred choice for this patient?

Explanation

## Castration-Resistant Prostate Cancer (CRPC) Management ### Definition and Pathophysiology Castration-resistant prostate cancer is defined as: - Biochemical or radiological progression despite castrate testosterone levels (<50 ng/dL) - Continued androgen receptor (AR) signaling despite ADT - Mechanisms: AR amplification, AR mutations, intratumoral androgen synthesis, alternative AR ligands **Key Point:** Abiraterone acetate is a CYP17A1 inhibitor that blocks both testicular and intratumoral androgen synthesis, making it the preferred next-line agent for mCRPC after progression on conventional ADT. ### Mechanism of Abiraterone Abiraterone acetate inhibits **17α-hydroxylase/17,20-lyase (CYP17A1)**, a critical enzyme in the androgen synthesis pathway: ```mermaid flowchart TD A[Cholesterol]:::outcome --> B[Pregnenolone]:::outcome B --> C[17-OH Pregnenolone]:::outcome C -->|CYP17A1 inhibited by Abiraterone| D[DHEA]:::outcome D --> E[Androstenediol]:::outcome E --> F[Testosterone]:::urgent F --> G[DHT]:::urgent style A fill:#e8f4f8 style F fill:#ffe8e8 style G fill:#ffe8e8 ``` **High-Yield:** Abiraterone blocks androgen synthesis at **multiple sites**: - Adrenal glands (primary) - Testes (secondary) - Tumor microenvironment (intratumoral synthesis) This is superior to first-generation antiandrogens (flutamide, nilutamide, cyproterone) which only block AR binding but do NOT reduce circulating testosterone. ### Comparison: Next-Line Hormonal Agents in mCRPC | Agent | Class | Mechanism | Efficacy in mCRPC | Current Role | |-------|-------|-----------|-------------------|---------------| | **Abiraterone acetate** | CYP17 inhibitor | Blocks adrenal & intratumoral androgen synthesis | **Proven OS benefit (COU-AA-302)** | **First-line for mCRPC** | | **Enzalutamide** | AR antagonist (2nd-gen) | Blocks AR nuclear translocation & DNA binding | Proven OS benefit (AFFIRM trial) | Alternative to abiraterone | | **Flutamide** | AR antagonist (1st-gen) | Blocks AR binding only | Inadequate in CRPC | Obsolete for CRPC | | **Nilutamide** | AR antagonist (1st-gen) | Blocks AR binding only | Inadequate in CRPC | Obsolete for CRPC | | **Cyproterone acetate** | AR antagonist + progestin | Blocks AR + GnRH (hepatotoxicity) | Inadequate in CRPC | Not used in CRPC | **Clinical Pearl:** Abiraterone requires concurrent prednisone (5–10 mg daily) to prevent mineralocorticoid excess (hypokalemia, hypertension) caused by accumulation of upstream steroid precursors. **Mnemonic:** **"CRPC = CYP17 inhibitor"** — Abiraterone (CYP17 inhibitor) is the paradigm shift from first-generation antiandrogens in CRPC because it addresses the fundamental problem: continued androgen synthesis despite castrate testosterone. **Tip:** Distinguish: - **Hormone-sensitive prostate cancer (HSPC)** → GnRH agonist ± first-gen antiandrogen - **mCRPC (newly diagnosed)** → Abiraterone or enzalutamide (both improve OS) - **mCRPC (post-abiraterone)** → Enzalutamide or cabazitaxel [cite:Harrison 21e Ch 89]