Adjuvant Therapy in High-Risk Prostate Cancer

FDA-Approved Indications and Guidelines

• The National Comprehensive Cancer Network recommends abiraterone acetate (1000 mg daily) combined with prednisone for metastatic castration-resistant prostate cancer (mCRPC) - Category 1 recommendation 1
• The European Association of Urology recommends abiraterone (for 2 years) combined with ADT (for 3 years) and whole-pelvic radiation therapy for cN1 patients, demonstrating improved metastasis-free survival (82% vs 69% at 6 years) and overall survival (HR 0.60, p<0.001) 2

Standard of Care for High-Risk Localized Prostate Cancer

• The standard of care for patients with high-risk localized prostate cancer (T3a, Gleason 8-10, or PSA >20 ng/mL) is external beam radiation therapy (EBRT) + long-term ADT (2-3 years), achieving 9-year disease-specific survival of 91% with trimodality therapy, as per Praxis Medical Insights guidelines, however an alternative guideline is preferred 3
• An alternative to the above is Radical prostatectomy with pelvic lymph node dissection, for selected patients only, achieving 36% progression-free survival for Gleason 8-10 disease, however the guideline society for this is not specified 3

Critical Clinical Considerations

• The American College of Cardiology is not mentioned, however, The National Comprehensive Cancer Network recommends monitoring for toxicity if abiraterone is used in approved settings: hypertension (21% grade 3-4), hypokalemia (12% grade 3-4), and hepatotoxicity require regular monitoring of blood pressure, electrolytes, and liver function 1
• The National Comprehensive Cancer Network also notes that patients ≥70 years experience increased toxicities with abiraterone (47% vs 33% grade 3-5 adverse events) and may have attenuated survival benefits 1

Abiraterone Therapy in High-Risk Locally Advanced Prostate Cancer

Introduction to Abiraterone Therapy

• The American Society of Clinical Oncology (ASCO) recommends abiraterone acetate (1000 mg daily) combined with prednisone (5 mg daily) and androgen deprivation therapy (ADT) for patients with high-risk locally advanced non-metastatic prostate cancer who are receiving radiotherapy, based on strong evidence demonstrating improved metastasis-free survival (82% vs 69% at 6 years) and overall survival (HR 0.60) 4

Patient Selection Criteria

• Patients with node-positive disease (cN1) or node-negative disease with at least 2 high-risk features are eligible for abiraterone therapy, provided they are receiving radiotherapy, as recommended by ASCO 4

Contraindications and Exclusions

• Abiraterone should not be offered to patients with locally advanced disease who are not receiving radiotherapy, as the evidence specifically requires radiotherapy as part of the treatment plan, according to the National Comprehensive Cancer Network (NCCN) 4
• The NCCN also recommends not offering abiraterone to patients who have already progressed to castration-resistant disease, as this is a different indication 5

Disease Definition and Treatment Context

• The use of abiraterone is critical in distinguishing locally advanced disease, and radiotherapy must be planned or delivered, as stated by ASCO 4
• The LATITUDE high-risk definition does not apply to locally advanced disease, but rather to metastatic disease, as noted by the Journal of Clinical Oncology 6

Abiraterone Therapy for High-Risk Prostate Cancer

Patient Eligibility and Treatment

• The National Comprehensive Cancer Network recommends adding abiraterone to radiation plus androgen deprivation therapy (ADT) for patients with T3aN0M0 prostate adenocarcinoma and high-risk criteria, including at least 2 of the following: T3-T4 stage, PSA >40 ng/mL, or Gleason score 8-10 7
• For patients with confirmed T3a disease and Gleason 4+3, abiraterone 1000 mg daily plus prednisone 5 mg daily for 24 months is recommended in combination with radiation therapy and ADT for 24-36 months if the patient meets the high-risk criteria 7

Evidence and Outcomes

• The STAMPEDE trial demonstrated significant survival benefit with abiraterone in patients with high-risk N0M0 disease, with an overall survival hazard ratio of 0.63 (95% CI 0.5-0.76, P<0.0001) 8
• Failure-free survival improved dramatically in the M0 subset (HR 0.21, P<0.0001) 8
• Abiraterone was given for 2 years when combined with curative-intent radiation in non-metastatic disease 8

Treatment Duration and Monitoring

• Abiraterone acetate 1000 mg once daily on an empty stomach plus prednisone 5 mg once daily for 24 months is recommended 7
• Continue abiraterone for 2 years in combination with radiation and ADT (which continues for 24-36 months total) 8
• Mandatory monitoring includes baseline and ongoing assessment of blood pressure, serum potassium, liver function tests, and cardiac evaluation 7

Adverse Events

• Mineralocorticoid excess effects, including hypertension (21% grade 3-4), hypokalemia (12% grade 3-4), and edema, are expected adverse events 7
• Hepatotoxicity requiring regular liver function monitoring (7% grade 3-5) is a potential adverse event 7
• Cardiac disorders, including atrial fibrillation (rare but increased), are potential adverse events 7
• Overall discontinuation rate due to adverse events is approximately 12% 7

Abiraterone + ADT + Radiotherapy for Very High‑Risk Non‑Metastatic Prostate Cancer

Evidence of Efficacy

• In patients with very high‑risk M0 prostate cancer (N1 disease or ≥ 2 of: T3‑T4 stage, PSA > 40 ng/mL, Gleason 8‑10), adding abiraterone acetate to ADT and concurrent whole‑pelvic radiotherapy improves 6‑year metastasis‑free survival to 82 % versus 69 % (HR 0.53, P < 0.0001). ESMO 2023 supports this benefit. 9

Patient Eligibility

• Candidates must be receiving curative‑intent external‑beam radiotherapy and possess at least two high‑risk features (e.g., T3‑T4 stage, PSA > 40 ng/mL, Gleason 8‑10). These criteria define the “very high‑risk” population studied. 9

Treatment Regimen

• Abiraterone acetate 1000 mg orally once daily on an empty stomach for 24 months.
• Prednisone 5 mg orally once daily for 24 months.
• Androgen‑deprivation therapy continued for a total of 24–36 months (extending beyond abiraterone completion).
• Whole‑pelvic radiotherapy delivered concurrently with the above systemic therapy. All components are based on the STAMPEDE trial protocol for non‑metastatic disease. 9, 10

Duration Rationale

• The 2‑year abiraterone course is specifically established for non‑metastatic disease receiving curative‑intent radiation; in metastatic disease the drug is continued until disease progression. 10

Guideline Recommendations

• ESMO (2023) – Level I, Grade B recommendation for external‑beam RT + ADT + abiraterone‑prednisone in very high‑risk M0 disease, specifying the 24‑month abiraterone and 24–36‑month ADT schedule. 9
• ASCO (2021) – Strong recommendation (high‑quality evidence) to add abiraterone to ADT for men with non‑castrate advanced prostate cancer undergoing radiotherapy. For metastatic patients the drug is given until progression, whereas for M0 disease the duration is limited to 24 months. 11, 10, 12

Safety & Practical Pitfalls

• Do not extend abiraterone beyond 24 months in the non‑metastatic setting; longer treatment is reserved for metastatic disease. 10
• Do not use the micronized formulation of abiraterone for non‑castrate disease, as it lacks FDA approval for this indication. 10
• Administer abiraterone on an empty stomach to ensure consistent bioavailability; food markedly reduces absorption. 10

Comparison with Alternative Systemic Options

• Docetaxel + ADT is not recommended for locally advanced non‑metastatic prostate cancer because it provides less survival benefit than abiraterone in this setting. STAMPEDE data demonstrate superior outcomes with abiraterone compared with docetaxel for very high‑risk M0 disease. 13, 12

Concurrent Initiation and Management of ADT, Abiraterone, and Radiotherapy in High‑Risk Locally Advanced Prostate Cancer

Timing of Androgen Deprivation Therapy (ADT) Initiation

• Initiate ADT first, ideally 2–4 weeks before adding abiraterone and radiotherapy to allow adequate testosterone suppression in patients with high‑risk locally advanced prostate cancer. 14

Duration of Abiraterone Therapy

• In non‑metastatic disease receiving curative‑intent radiotherapy, abiraterone should be given for a fixed 24‑month course; extending treatment beyond this period is not recommended. In metastatic castration‑resistant disease, abiraterone is continued until disease progression. [15][14]

Mandatory Monitoring During Concurrent Therapy

• Hypertension develops in approximately 22 % of patients (severe hypertension in about 4 %). 15
• Hypokalemia occurs in roughly 17 % of patients. 15
• Hypophosphatemia is observed in about 24 % of patients. 15
• Elevations of liver enzymes (ALT/AST) lead to treatment discontinuation in 11–12 % of patients. 15
• Cardiac events are reported in 19 % of patients, including atrial fibrillation in 4 %. 15

Guideline Consensus and Strength of Recommendation

• The American Society of Clinical Oncology (ASCO, 2021) and the European Society for Medical Oncology (ESMO, 2023) issue strong recommendations (high‑quality evidence) to add abiraterone to ADT for men with high‑risk locally advanced prostate cancer who are also receiving radiotherapy, with the requirement that all three modalities be delivered concurrently. 14

Historical Guidelines and Outcome Evidence for Adjuvant Abiraterone in High‑Risk Prostate Cancer

NCCN Guideline (2010)

• The 2010 NCCN guideline for high‑risk prostate cancer recommended definitive external‑beam radiotherapy combined with long‑term androgen‑deprivation therapy (2–3 years) for patients with T3a disease, Gleason grade 8–10, or markedly elevated PSA, without the addition of abiraterone. 16

Comparative Survival Outcomes

• In the pre‑abiraterone era, radiotherapy plus long‑term ADT alone achieved a 10‑year overall survival of approximately 45 % among patients with Gleason 8–10 disease and a 9‑year disease‑specific survival of about 91 % when trimodality therapy was used. 17

• Incorporating adjuvant abiraterone to the radiotherapy‑ADT regimen yields a measurable survival advantage, demonstrated by a 6‑year overall‑survival hazard ratio of 0.60 (40 % reduction in risk of death) compared with ADT alone. 18