William Lee

<h4>Background</h4>Evolving data suggest that men with high-risk localized prostate cancer may benefit from more potent androgen receptor inhibition in the context of curative intent radiotherapy. Recently updated American Society for Clinical Oncology (ASCO) evidence-based guidelines and the National Comprehensive Cancer Network (NCCN) Guidelines have updated recommendations for the consideration of adding second generation anti-androgens to androgen deprivation therapy (ADT) in men receiving radiation therapy (RT) for noncastrate locally advanced high and very high risk nonmetastatic or node positive prostate cancer.<h4>Methods and results</h4>We conducted a comprehensive review of existing published and abstract presented evidence behind RT with ADT for the definitive management of high-risk prostate cancer, particularly focused on the current phase II and III trial evidence for the addition of second generation anti-androgens to ADT in definitive RT treatment of high-risk prostate cancer and specifically focused on the recent STAMPEDE trial results with abiraterone acetate. We review the biological mechanisms in which second generation anti-androgens may help mitigate ADT resistance and provide radiosensitization through inhibition of DNA repair. Finally, we discuss ongoing clinical trials of potent androgen receptor (AR) inhibitors with ADT in this non-metastatic high-risk radiotherapy setting that may inform on future treatment guidelines.<h4>Conclusions</h4>Recent data suggest an overall survival benefit as well as increased probabilities of disease free and metastasis free survival in men with high and very high-risk localized, node positive, and oligometastatic hormone sensitive prostate cancer with abiraterone acetate and prednisone and support the use of potent AR inhibitors in this setting after informed decision making.

BACKGROUND: Moderately hypofractionated radiotherapy (MHRT) is an accepted treatment for localized prostate cancer; however, limited MHRT data address high-risk prostate cancer (HRPC) and/or African American patients. We report clinical outcomes and toxicity profiles for individuals with HRPC treated in an equal access system. METHODS: We identified patients with HRPC treated with MHRT at a US Department of Veterans Affairs referral center. Exclusion criteria included < 12 months follow-up and elective nodal irradiation. MHRT included 70 Gy over 28 fractions or 60 Gy over 20 fractions. Acute and late gastrointestinal (GI) and genitourinary (GU) toxicities were graded using Common Terminology Criteria for Adverse Events, version 5.0. Clinical endpoints, including biochemical recurrence-free survival (BRFS), distant metastases-free survival (DMFS), overall survival (OS), and prostate cancer-specific survival (PCSS) were estimated using Kaplan-Meier methods. Clinical outcomes, acute toxicity, and late toxicity-free survival were compared between African American and White patients with logistic regression and log-rank testing. RESULTS: Between November 2008 and August 2018, 143 patients with HRPC were treated with MHRT and followed for a median of 38.5 months; 82 (57%) were African American and 61 were White patients. Concurrent androgen deprivation therapy (ADT) was provided for 138 (97%) patients for a median duration of 24 months. No significant differences between African American and White patients were observed for 5-year OS (73% [95% CI, 58%-83%] vs 77% [95% CI, 60%-97%]; P = .55), PCSS (90% [95% CI, 79%-95%] vs 87% [95 % CI, 70%-95%]; P = .57), DMFS (91% [95% CI, 80%-96%] vs 81% [95% CI, 62%-91%]; P = .55), or BRFS (83% [95% CI, 70%-91%] vs 71% [95% CI, 53%-82%]; P = .57), respectively. Rates of acute grade 3+ GU and GI were low overall (4% and 1%, respectively). Late toxicities were similarly favorable with no significant differences by race. CONCLUSIONS: Individuals with HRPC treated with MHRT in an equal access setting demonstrated favorable clinical outcomes that did not differ by race, alongside acceptable rates of acute and late toxicities.

<h4>Purpose/objective(s)</h4>Androgen deprivation therapy (ADT) and radiotherapy (RT) are synergistic, and the combination results in improved survival outcomes for aggressive prostate cancers. However, long-term ADT carries substantial burden of toxicity and morbidity. We hypothesized that a combination of definitive prostate RT and short-term complete androgen blockade (CAB) in men with unfavorable intermediate or favorable high-risk localized PC would provide excellent biochemical control and allow high rates of testosterone recovery. This combination would allow an escalation of therapy for unfavorable intermediate risk and de-escalation for favorable high-risk patients. We tested this hypothesis in a prospective trial of neoadjuvant/concurrent/adjuvant abiraterone acetate, prednisone, and LHRH agonist given for 6 months in conjunction with definitive prostate external beam RT. We now report the mature results of this trial.<h4>Materials/methods</h4>37 men were enrolled in an IRB-approved NCT-registered prospective multi-center single arm investigator-initiated trial between January 2014 and August 2016. Eligibility required unfavorable intermediate risk of low volume high risk (NCCN) prostate cancer. All men were treated with 6 months of abiraterone acetate (1000mg daily), prednisone (5mg daily), and depot LHRH agonist initiated 8 weeks prior to standard fractionation RT to prostate/seminal vesicles +/- pelvis. Endpoints included PSA and testosterone (T) kinetics, biochemical progression-free survival (PFS), metastasis-free survival (MFS), overall survival (OS), and patient-reported quality-of-life.<h4>Results</h4>Enrolled patients were low volume (T1-2 disease and PSAs < 20 ng/ml), with Grade Group 1 (11%), 2 (11%), 3 (35%), 4 (27%), and 5 (16%); 43% were high-risk. The median follow-up time among all 37 surviving patients is 58months (range 24-65). Treatment was well tolerated and has been reported previously. In the entire cohort, 5-year BPFS was 92% (95% CI 72-98%). 32 out of 37 men recovered T to at least 150 ng/dl; the median time to T recovery was 9.2 mo (95% CI: 9.0-12.2). In men with T recovery, the 5-year BPFS was also 92% (95% CI: 71-98%). Hormonal/sexual function declined at six months but had improved by 24 mo and remained stable thereafter.<h4>Conclusion</h4>For select men with aggressive prostate cancer, short course CAB with abiraterone acetate plus prednisone in combination with definitive prostate RT allows rapid T recovery and can provide excellent biochemical control up to 5 years. Short-course CAB is feasible for favorable high risk prostate cancer and may support optimization of patient quality of life. Prospective randomized trials should be considered.