Learning Objective

At the conclusion of the activity, participants will be able to discuss new treatment available for patients with newly diagnosed M1 prostate and new treatment available for patients with M0 metastatic castrate-resistant prostate cancer.

As the course director, I have been fortunate to host a course on advanced prostate cancer at the AUA Annual Meeting since 2012, and the changes over these 10+ years have been nothing less than spectacular!¹ Furthermore, the last several years have been “interesting,” with this being the first “live” AUA since 2019 due to COVID. It was exciting being back in front of a live audience. Furthermore, Dr. Karsh and I welcomed genitourinary medical oncologist superstar Dr. Alicia Morgans to the course, and she delivered a wonderful talk and great panel ­discussion.

In the years from 2012 to 2015, it was all about metastatic castrate-resistant prostate cancer (CRPC) with multiple new therapeutic advances starting in 2010 (sipuleucel-T) followed by abiraterone and enzalutamide and a focus on bone-targeted agents. Later, we expanded to cover hormone-sensitive (HS) advanced disease due to the new data on docetaxel and abiraterone extending survival in new M1 patients. In 2017, we added the topic of nonmetastatic CRPC (M0 CRPC) due to emerging data on use of apalutamide and enzalutamide in these men, and data now suggest similar benefit for adding darolutamide as well. Then in 2019, we doubled down on HS new M1 disease with emerging data that 4 agents (docetaxel, abiraterone, apalutamide, and enzalutamide) all improve survival for men with new metastatic prostate cancer.

Now, from 2020 to 2022, we have been going boldly into personalized molecular medicine with the addition of both hereditary and somatic testing for cancer-associated gene alterations and several therapeutic agents U.S. Food and Drug Administration (FDA)-­approved in the past several years based on this molecular testing.

Newly Diagnosed HS M1 Prostate Cancer

Seven years ago hormone-naïve/HS newly diagnosed metastatic (M1) prostate cancer became hot news with the release of the CHAARTED trial data in 2015 and the STAMPEDE trial results in 2016 showing a benefit of up-front docetaxel chemotherapy in new M1 disease.^2,3 Primary androgen deprivation therapy (ADT) had been the only treatment for men with new M1 disease for more than three-quarters of a century. In the last few years CHAARTED and STAMPEDE taught us that adding 6 cycles of docetaxel within 4 months of starting hormone therapy/ADT resulted in a major survival benefit. For high-volume disease (4 or more bone metastases and/or visceral metastases) the addition of chemotherapy resulted in a 17-month survival advantage compared to ADT alone. However, the initial publication hazard ratio generally supported a benefit of docetaxel for low-volume M1 disease as well. The STAMPEDE trial confirmed the benefit of docetaxel and generally supported the use of chemotherapy for all men with new M1 disease. Median overall survival (OS) was 65 months for men randomized to receive docetaxel vs 43 months for men randomized to standard of care ADT alone. In 2018, Kyriakopoulos et al reported longer-term followup from CHAARTED confirming the benefit of docetaxel for high-volume disease but not supporting up-front chemotherapy for low-volume disease.⁴

In 2017 the LATITUDE trial showed that abiraterone added to ADT for men with new M1 disease resulted in a similar survival benefit to docetaxel.⁵ In 2019, we learned that both apalutamide and enzalutamide also significantly extend survival compared to traditional ADT alone.^6-8 The results of TITAN (apalutamide) and ENZAMET and ARCHES (NCT02677896; enzalutamide) were published showing robust benefits. In my mind, this is “combined androgen blockade” (CAB) or “maximal androgen blockade” (MAB) finally showing a survival benefit now using second- and third-generation nonsteroidal antiandrogens (AAs).⁹

In TITAN, 1,052 men were randomized to traditional ADT alone vs ADT plus apalutamide (240 mg orally daily).⁶ Ten percent received prior docetaxel, 80% had M1 disease at initial diagnosis, and 63% had high-volume disease. In the final analysis, at a median followup of 44 months, 51% remained on apalutamide.¹⁰ Apalutamide conferred a 35% reduction in risk of death. This benefit was present regardless of disease volume or receipt of docetaxel. At 4 years, OS was 65% in the apalutamide arm and 51.8% in the ADT plus placebo group.

In a similar fashion, ARCHES (NCT02677896) and ENZAMET documented a similar benefit to enzalutamide in new M1 HS disease.^7,8 ARCHES was the FDA-registration trial and enrolled 1,150 new M1 patients receiving testosterone suppression with or without docetaxel, stratified by high- or low-volume disease, with men randomized to enzalutamide (574) vs placebo (576). At ESMO 2021, Armstrong et al presented the latest trial update. As of the data cutoff of May 28, 2021, 397 (34.5%) patients remained on treatment, with a median followup of 44.6 months. The median treatment duration was 40.2 months on enzalutamide + ADT, 13.8 months on placebo + ADT, and 23.9 months for crossover patients. Enzalutamide + ADT extended survival vs placebo + ADT (HR 0.66; 95% CI 0.53–0.81; p <0.0001).

Apalutamide, darolutamide, and enzalutamide are second-generation nonsteroidal oral AAs and are more potent than first-generation agents (flutamide, nilutamide, and bicalutamide). In past times, adding first generation AA to ADT was called CAB or MAB. The latest studies of second-generation agents finally prove the concept of CAB/MAB, first proposed by Labrie and others in the mid-1980s.¹⁰

The latest concept discussed by Dr. Karsh at the 2022 course was “triplet” therapy for M1 disease. The PEACE-1 trial reported by Fizazi et al at ESMO 2021 studied ADT plus docetaxel plus abiraterone acetate/prednisone vs ADT plus docetaxel, finding a survival benefit of the triple therapy.¹¹ The OS benefit was seen across subgroups, including those with high-volume disease (HR 0.72, 95% CI 0.55–0.95) and low-volume disease (HR 0.83, 95% CI 0.50–1.38; data immature). Adding abiraterone acetate/prednisone to ADT plus docetaxel improves both radiographic progression-free survival and OS in ­metastatic castrate-sensitive prostate cancer men, even when 84% of metastatic CRPC men from the control arm received an androgen-signaling inhibitor. Toxicity was as expected—no new safety concerns were seen in this new triple combination treatment. From a clinical perspective, the benefit was a median lifetime gain of more than 1.5 years for metastatic castrate-sensitive prostate cancer men with high-volume disease (5.1 vs 3.5 years).¹¹ Finally, ARASENS is a phase III clinical trial of ADT plus docetaxel plus darolutamide vs ADT plus docetaxel plus placebo that was reported at ASCO GU in February 2022 by Dr. Matthew Smith.¹² There was an OS in favor of the triple therapy including darolutamide for both de novo M1 and recurrent M1 disease reported.

CRPC

Since 2010, multiple new agents have been approved by the FDA for M1 CRPC, including sipuleucel-T, cabazitaxel, abiraterone acetate, denosumab, enzalutamide, and radium-223. Except for cabazitaxel, all of these agents are commonly available for urologists and oncologists to prescribe. The latest advances are olaparib, rucaparib, and pembrolizumab for patients with somatic or germline mutations in actionable genes implicated in advanced prostate cancer.¹³–¹⁶

Bone Health/Denosumab

Denosumab (trade name Xgeva®) is prescribed at a dose of 120 mg subcutaneously monthly to prevent skeletal-related events in men with M1 CRPC with bone metastases.¹⁷ The FDA also approved a 60 mg dose (trade name Prolia®) subcutaneously twice a year to prevent bone loss (osteopenia and osteoporosis) in men without bone metastases who are on gonadotropin-releasing hormone analogue therapy for prostate cancer. We continue to remind urologists to be mindful of using supportive agents including vitamin D and calcium supplements, and monitoring for osteopenia and osteoporosis with annual dual energy x-ray absorptiometry scanning.

Sipuleucel-T

Sipuleucel-T is a novel immunotherapy approved by the FDA in 2010 for asymptomatic or minimally symptomatic M1 CRPC.¹⁸ The ideal patient for sipuleucel-T should have documented clinical metastases and a rising PSA while on continuous hormonal therapy. The patient should not have bone or cancer pain requiring narcotic pain medications. In men with PSA levels in the lowest quartile of the IMPACT trial (PSA less than 22 ng/ml) there was a more robust OS advantage to sipuleucel-T. Specifically, the estimated 3-year survival in this group of treated patients was 62.6% compared to 41.6% for men randomized to the control arm of the study.¹⁹ The PROSEED registry of 1,902 patients treated with sipuleucel-T in real-world practice between 2011 and 2014 has also provided confirmatory data. In a respective analysis of 219 African American men disease-matched to a Caucasian cohort, OS was 35.3 months vs 25.8 months.²⁰ These intriguing data need to be confirmed in prospective fashion.

Abiraterone

Abiraterone is a 17-lyase and 17-hydrolase inhibitor that blocks key pathways in the steroidal synthesis pathways leading to androgen production.²¹ Low-dose prednisone (5 to 10 mg daily is a physiological dose) is recommended to be administered with abiraterone to help limit overproduction of aldosterone and limit the side effects of hypertension, hypokalemia, and fluid retention. The FDA-approved indication for abiraterone is before or after docetaxel chemotherapy in men with M1 CRPC based on evidence from the Cougar-AA-301 and -302 clinical trials. The dose for abiraterone is 1,000 mg orally once daily in the fasted state along with low-dose steroid (5 mg prednisone orally twice daily). The final analyses of both trials were reviewed, showing clinically meaningful end points of OS and radiographic progression-free survival (Cougar-302) benefits. Abiraterone is also available in a 500 mg oral dose, which allows for 2 rather than 4 pills per day, which might help with compliance for some men.

Abiraterone was also FDA approved for use in men with newly diagnosed HS M1 prostate cancer in February 2018.²² Approval was based on LATITUDE (NCT01715285), a placebo-controlled international clinical trial that randomized 1,199 patients with metastatic high-risk HS disease. Patients received 1,000 mg abiraterone acetate orally once daily with 5 mg prednisone once daily (in 597) or matching placebos orally once daily (in 602). Patients in both arms received a gonadotropin-releasing hormone analogue or underwent bilateral orchiectomy. The major efficacy end point was OS. Median OS was inestimable and 34.7 months in the abiraterone acetate and placebos arms, respectively (HR 0.621; 95% CI 0.509, 0.756; p <0.0001). Median duration of abiraterone use was 24 months.

Enzalutamide

Enzalutamide, a second-generation androgen receptor antagonist, was FDA approved in 2012 to treat men with disease who progressed after docetaxel based chemotherapy based on level 1 evidence from the AFFIRM trial.²³ It received expanded approval in 2014 for use before chemotherapy in the PREVAIL trial. Enzalutamide is taken orally at a dose of 160 mg daily with or without food and it does not require prednisone. However, enzalutamide does have an approximately 0.5%–1% risk of seizures associated with its use and crosses the blood-brain barrier, implicating it with some risk of falls and fatigue.

PROSPER is a phase III, randomized, double-blind, placebo-controlled study of enzalutamide in men with M0 CRPC.²⁴ It demonstrated an approximately 2-year ­metastasis-free survival (MFS) benefit over placebo, showing that MFS is a meaningful end point. As of July 13, 2018, enzalutamide was the second FDA-approved drug for M0 CRPC. Updated data from PROSPER in 2020 confirmed an OS benefit.²⁵

In the setting of M1 HS disease, enzalutamide is also FDA approved based on ARCHES and ENZAMET, as noted earlier.

Apalutamide

As previously noted, apalutamide, with a mechanism of action similar to enzalutamide, was the first drug for M0 CRPC approved by the FDA, which occurred in February 2018.²⁶ The data from the SPARTAN trial showed that apalutamide delayed MFS by about 2 years. Overall the drug was very well tolerated. Unique side effects included maculopapular rash in 24% of patients, but only 5% were grade 3–4. The rash usually resolved with topical lotions, drug holiday, and temporary dose reduction. Approximately 4% of patients required systemic corticosteroids. In addition, 8% of patients had decreases in thyroid hormone (considered chemical hypothyroidism), and there were no grade 3–4 adverse events. The FDA did not mandate thyroid testing in the approval label. Seizure was reported in 2 patients (0.2%).

Apalutamide, as noted earlier, was also proven to extend survival in newly diagnosed HS M1 prostate cancer, and final analysis of the TITAN trial showed a robust 35% improvement in OS compared to ADT alone. The TITAN trial is credited with finally proving the OS benefit of CAB, ending a quest of 30+ years to prove this concept.

Another topic of interest related to use of abiraterone and enzalutamide/apalutamide is molecular profiling. The discovery of the AR-V7 splice variant of the androgen receptor offers an intriguing glimpse of the future of personalized medicine.²⁷ Specifically, the response to abiraterone or enzalutamide was less robust in men who harbored this variant in circulating tumor cells. In February 2018 Genomic Health, Inc. (Redwood City, California) received FDA approval for the Oncotype DX® AR-V7 Nucleus Detect™ test, a commercially available assay for AR-V7.

Radium-223

Radium-223 is a parenteral radiopharmaceutical that can be ordered by urologists. It is usually given in a nuclear medicine or radiation oncology department setting, but many large group practices have incorporated it into their centers. It is an alpha-emitting liquid radiation product that received FDA approval in May 2013 based on results from the ALSYMPCA trial.²⁸ Radium-223 is indicated for the treatment of patients with symptomatic M1 CRPC with bone metastases and no known visceral metastatic disease. The dose regimen is 50 kBq (1.35 microcurie) per kg body weight, given at 4-week intervals in 6 injections.

Urologists may be familiar with earlier generation beta radiopharmaceuticals such as samarium and strontium. However, radium-223 is different. It is a large molecule alpha particle and does not penetrate the bone marrow to the degree of older agents. In other words, radium-223 is much less likely to cause serious bone marrow toxicity. In addition, the use of radium-223 was associated with an OS benefit whereas the older beta-emitting radiopharmaceuticals were never proven to extend survival. For radium-223 to be associated with improved survival at least 4 monthly cycles must be administered.

Radium-223 should not be used in patients currently being treated with abiraterone/prednisone. The phase III ERA223 trial compared abiraterone/prednisone plus radium-223 vs abiraterone/prednisone plus placebo in patients with asymptomatic or mildly symptomatic chemotherapy-naïve metastatic CRPC. The study was unblinded in late 2017. Bayer, the manufacturer of radium-223, reported that the unblinding followed the recommendation of an independent data monitoring committee that observed an imbalance, with more fractures and deaths in patients receiving radium-223 and abiraterone/prednisone vs abiraterone alone.²⁹

Darolutamide

In mid-2019, darolutamide was FDA approved for M0 CRPC based on the ARAMIS trial, making this the third agent approved (apalutamide, enzalutamide, and darolutamide) in this disease state.³⁰ This third-generation nonsteroidal oral AA prolonged MFS also by approximately 2 years compared to placebo in M0 CRPC and more recently showed an OS advantage.³¹ The drug has twice daily oral dosing, which may be a slight disadvantage compared to enzalutamide and apalutamide, but does not appear to cross the blood-brain barrier to the extent of the other 2 agents and is reportedly less apt to cause falls and seizures, and might even result in less fatigue and fractures. Darolutamide is also under study for M1 HS prostate cancer with the ARASENS trial, as noted earlier in this article. This interesting trial design compares ADT plus darolutamide plus 6 cycles of docetaxel vs ADT plus docetaxel plus placebo, and in 2022 reported an OS benefit of the triple therapy including darolutamide vs ADT plus docetaxel alone.

Molecular Profiling and Novel Therapeutics

Current AUA and National Comprehensive Cancer Network® guidelines recommend germline and somatic testing for men with advanced prostate cancer. About 12% of men with M1 prostate cancer will harbor actionable germline mutations, and about 25% of men with CRPC will have actionable somatic mutations. Most common are BRCA, ATM, and CHEK2. In 2021, there are 3 new drugs approved to treat men with actionable mutations: olaparib (Lynparza®, AstraZeneca), rucaparib (Rubraca®, Clovis Oncology), and pembrolizumab (Keytruda®, Merck).^13-16

Rucaparib is a PARP inhibitor that is approved for patients who had BRCA1/2 alterations, in patients with disease progression after an androgen receptor signaling inhibitor and docetaxel. Olaparib offers a survival benefit (from the PROFOUND trial) for patients with homologous recombination repair mutations after progression of disease on an androgen receptor signaling inhibitor, and does not mandate prior receipt of docetaxel chemotherapy. Indications for olaparib include the following homologous recombination repair mutations: BRCA 1/2 ATM, CDK12, CHEK2, CHEK1, BARD1, BRIP1, FANCL, PALB2, RAD51B, RAD51C, RAD51D, and RAD54L. Pembrolizumab has an agnostic indication for all solid tumors that are tested positive for microsatellite instability-high and tumor mutation burden >10.¹³–¹⁶

Summary

The management of advanced prostate cancer continues to evolve in exciting and sometimes unexpected ways, and 2022 has brought further options to our patients, including abiraterone, enzalutamide, and apalutamide in newly diagnosed, HS M1 prostate cancer, as well as apalutamide, enzalutamide, and darolutamide for M0 CRPC. The personalized medicine era is upon us also with approval of 3 agents for patients with actionable germline or somatic mutations. Interested readers should review the latest AUA guidelines on this topic.^32,33