Comparative Efficacy of AR Inhibitors

May 5, 2026

Comparative evidence: enzalutamide vs abiraterone or other AR pathway inhibitors

Enzalutamide and abiraterone provide similar overall survival in prostate cancer, but enzalutamide shows modest advantages for progression endpoints in castration-resistant disease, and sequencing from abiraterone to enzalutamide yields better outcomes than the reverse order due to preserved second-line activity.

Abstract

Ten studies including direct randomized trials, crossover studies, and network meta-analyses compared AR pathway inhibitors across metastatic castration-resistant, hormone-sensitive, and high-risk nonmetastatic prostate cancer settings. In metastatic CRPC, indirect comparisons found no significant overall survival difference between enzalutamide and abiraterone (HR 1.03, 95% CI 0.854-1.242), though enzalutamide demonstrated superior radiographic progression-free survival (HR 0.516, 95% CI 0.438-0.608), time to PSA progression (HR 0.365, 95% CI 0.303-0.441), and PSA response rates (RR 0.69, 95% CI 0.61-0.79, p<0.00001). Sequencing order materially affects outcomes: abiraterone followed by enzalutamide achieved longer time to second progression (19.3 versus 15.2 months, HR 0.66, p=0.036) than the reverse sequence, driven by markedly asymmetric second-line activity (36% PSA response for enzalutamide post-abiraterone versus 4% for abiraterone post-enzalutamide). Combining enzalutamide with abiraterone provided no survival benefit over enzalutamide alone (median OS 32.7 versus 33.6 months, p=0.53) while increasing grade 3-5 toxicity (68.8% versus 55.6%). In hormone-sensitive disease, network meta-analysis found no significant differences between ARPi agents in most contexts, though enzalutamide showed advantage in low-volume disease. Safety profiles were broadly similar, though enzalutamide ranked most toxic for hypertension across disease settings and increased fatigue risk (RR 0.45, 95% CI 0.24-0.85). The evidence supports similar overall survival with modest enzalutamide advantages for progression endpoints in CRPC, favors abiraterone-first sequencing, and suggests treatment selection should consider disease volume, sequencing strategy, and toxicity profiles rather than efficacy differences alone.

Methods

We analyzed 10 sources from an initial pool of 200, using 9 screening criteria. Each paper was reviewed for 7 key aspects that mattered most to the research question.

Characteristics of Included Studies

The systematic review included 10 studies comparing AR pathway inhibitors in prostate cancer across different disease settings and lines of therapy.

The studies varied considerably in treatment context. Two studies evaluated post-docetaxel mCRPC populations, while others examined first-line therapy in hormone-sensitive disease. Three studies were meta-analyses using indirect comparisons, while others were direct head-to-head RCTs. Disease settings ranged from metastatic CRPC to hormone-sensitive disease to high-risk nonmetastatic prostate cancer.

Overall Survival

Overall survival data showed variable results across different disease contexts and treatment lines. In metastatic CRPC patients previously treated with docetaxel, cabazitaxel demonstrated superior overall survival compared to switching to an alternative AR pathway inhibitor, with median OS of 13.6 versus 11.0 months (HR 0.64, 95% CI 0.46-0.89, p=0.008).

When comparing sequencing strategies, the abiraterone-first followed by enzalutamide sequence showed numerically longer overall survival (28.8 months) compared to the reverse sequence (24.7 months), though this difference was not statistically significant (HR 0.79, 95% CI 0.54-1.16, p=0.23).

The combination of enzalutamide plus abiraterone did not improve overall survival compared to enzalutamide alone in metastatic CRPC, with median OS of 32.7 months versus 33.6 months (p=0.53). This finding indicates no additive survival benefit from combining these agents.

In high-risk nonmetastatic prostate cancer, combination therapy with abiraterone and prednisolone (with or without enzalutamide) significantly improved overall survival compared to ADT alone (HR 0.60, 95% CI 0.48-0.73, p<0.0001). Prostate cancer-specific survival was also improved (HR 0.49, 95% CI 0.37-0.65, p<0.0001).

Meta-analyses comparing abiraterone and enzalutamide to placebo found similar overall survival benefits: abiraterone HR 0.69 (95% CI 0.60-0.80, p<0.00001) and enzalutamide HR 0.67 (95% CI 0.59-0.75, p<0.00001). Indirect comparison showed no significant difference in overall survival between abiraterone and enzalutamide (HR 1.03, 95% CI 0.854-1.242).

In metastatic hormone-sensitive prostate cancer, network meta-analysis found enzalutamide+ADT had the lowest absolute hazard ratio (0.53, 95% CI 0.37-0.75) with 76.9% probability of being the preferred treatment for overall survival. Enzalutamide showed better OS compared to docetaxel in men with low-volume disease, though no differences emerged in other comparisons.

Progression-Free Survival

Progression-free survival outcomes varied substantially by disease setting and prior treatment. In post-docetaxel mCRPC, cabazitaxel achieved superior imaging-based PFS (median 8.0 months) compared to switching to an alternative AR inhibitor (3.7 months), with HR 0.54 (95% CI 0.40-0.73, p<0.001). Median clinical PFS was 4.4 versus 2.7 months (HR 0.52, 95% CI 0.40-0.68, p<0.001).

Enzalutamide demonstrated marked superiority over bicalutamide, with median PFS of 19.4 versus 5.7 months (HR 0.24, 95% CI 0.18-0.32, p<0.001). Radiographic PFS in metastatic patients also favored enzalutamide (HR 0.32, 95% CI 0.21-0.50, p<0.001).

In the sequencing trial, time to second PSA progression was significantly longer with abiraterone→enzalutamide (19.3 months) versus enzalutamide→abiraterone (15.2 months), with HR 0.66 (95% CI 0.45-0.97, p=0.036).

Meta-analysis comparing abiraterone and enzalutamide to placebo revealed differential radiographic PFS benefits: abiraterone HR 0.64 (95% CI 0.57-0.71, p<0.0001) versus enzalutamide HR 0.33 (95% CI 0.29-0.37, p<0.00001). Indirect comparison suggested enzalutamide superiority for rPFS (HR 0.516, 95% CI 0.438-0.608).

In high-risk nonmetastatic prostate cancer, combination therapy significantly improved progression-free survival (HR 0.44, 95% CI 0.36-0.54, p<0.0001) and metastasis-free survival (HR 0.53, 95% CI 0.44-0.64, p<0.0001), with 6-year metastasis-free survival of 82% versus 69% for controls.

In metastatic hormone-sensitive prostate cancer, disease volume affected comparative efficacy. For high-volume disease, radiographic PFS hazard ratios were: abiraterone+ADT 0.46 (95% CI 0.40-0.53), enzalutamide+ADT 0.48 (0.41-0.56), apalutamide+ADT 0.53 (0.41-0.68), and darolutamide+ADT 0.60 (0.44-0.81). In low-volume disease, darolutamide+ADT showed the best numerical result (HR 0.30, 95% CI 0.15-0.60), with enzalutamide significantly better than abiraterone (HR 0.67, 95% CI 0.47-0.96).

PSA Response and Biochemical Outcomes

PSA response rates demonstrated notable variation across comparisons. Cabazitaxel achieved 35.7% PSA response versus 13.5% for AR pathway inhibitors (p<0.001). Enzalutamide showed substantially higher response rates than bicalutamide: 81% versus 31% for ≥50% PSA decline (p<0.001).

In the sequencing trial, first-line PSA response rates were 68% for abiraterone versus 82% for enzalutamide (p=0.023). On second-line therapy, enzalutamide demonstrated superior activity with 36% PSA response versus only 4% for abiraterone (p<0.0001).

Time to PSA progression also favored enzalutamide over bicalutamide (HR 0.19, 95% CI 0.14-0.26, p<0.001). Meta-analysis found enzalutamide superior to abiraterone for time to PSA progression: abiraterone HR 0.52 (95% CI 0.45-0.59) versus enzalutamide HR 0.19 (0.17-0.22) compared to placebo, yielding an indirect comparison HR of 0.365 (95% CI 0.303-0.441) favoring enzalutamide.

One meta-analysis specifically comparing PSA response rates found enzalutamide significantly superior to abiraterone (RR 0.69, 95% CI 0.61-0.79, p<0.00001).

Biochemical failure-free survival in high-risk nonmetastatic disease was significantly prolonged with combination therapy: median not reached for combination versus 86 months for controls (HR 0.39, 95% CI 0.33-0.47, p<0.0001).

Tumor Response

Objective tumor response rates were reported in limited studies. Cabazitaxel achieved 36.5% tumor response versus 11.5% for AR pathway inhibitors (p=0.004) in post-docetaxel mCRPC.

Safety and Tolerability

Overall adverse event rates showed considerable variation across studies. In the cabazitaxel comparison, grade 3 or higher adverse events occurred in 56.3% receiving cabazitaxel versus 52.4% receiving AR pathway inhibitors.

The enzalutamide plus abiraterone combination resulted in higher grade 3-5 adverse event rates (68.8%) compared to enzalutamide alone (55.6%), with higher treatment discontinuation rates (12% versus 5%).

In high-risk nonmetastatic disease, grade 3 or higher adverse events occurred in 37% of patients receiving abiraterone and prednisolone versus 58% receiving the triple combination with enzalutamide. The most common severe adverse events were hypertension (5% versus 14%) and alanine transaminitis (6% versus 13%). Seven grade 5 events occurred across combination arms: three with abiraterone (rectal adenocarcinoma, pulmonary hemorrhage, respiratory disorder) and four with triple therapy (septic shock and sudden death).

The sequencing trial revealed differential tolerability patterns. Hypertension (grade 3-4) was more common with abiraterone-first (27%) versus enzalutamide-first (18%). Dose modifications were required more frequently for enzalutamide during both first-line (18%) and second-line therapy (19%) compared to abiraterone (6% first-line, 5% second-line). No treatment-related deaths occurred.

Meta-analysis comparing abiraterone and enzalutamide found no significant difference in total adverse events (RR 0.42, 95% CI 0.14-1.31, p=0.14). However, enzalutamide was associated with higher fatigue risk (RR 0.45, 95% CI 0.24-0.85, p=0.01), while perceived cognitive impairment rates were similar (RR 0.94, 95% CI 0.47-1.88, p=0.85).

Network meta-analysis of adverse events found that ARSi side-effect profiles generally did not differ significantly, with one notable exception: enzalutamide ranked as most toxic for hypertension in both mCRPC (SUCRA 0%) and nmCRPC (SUCRA 0%), and for headache across all prostate cancer settings (mCRPC SUCRA 0%, nmCRPC SUCRA 1%, mCSPC SUCRA 3%).

Synthesis

The apparent contradictions in comparative efficacy between enzalutamide and abiraterone can be reconciled by examining context-specific factors.

Disease Setting and Treatment Line
The superiority of enzalutamide over abiraterone for certain endpoints appears most consistent in mCRPC populations. Meta-analyses demonstrated enzalutamide’s advantage for radiographic PFS (HR 0.516 favoring enzalutamide) and time to PSA progression (HR 0.365 favoring enzalutamide), while finding no difference in overall survival. This pattern suggests enzalutamide may delay disease progression more effectively in CRPC, but this does not necessarily translate to survival prolongation, possibly due to effective subsequent therapies or competing mortality risks.

In hormone-sensitive disease, the comparative picture changes. Network meta-analysis in mHSPC found no significant differences between ARPi agents in most settings, though enzalutamide showed significant rPFS benefit over abiraterone specifically in low-volume (HR 0.67, 95% CI 0.47-0.96) and synchronous disease (HR 0.73, 95% CI 0.59-0.89). This suggests disease volume and timing of metastases modify comparative efficacy.

Sequencing Effects and Cross-Resistance
The crossover trial provides mechanistic insight into differential activity patterns. While first-line PSA response rates favored enzalutamide (82% versus 68%), second-line responses revealed marked asymmetry: 36% for enzalutamide after abiraterone versus only 4% for abiraterone after enzalutamide. This 9-fold difference indicates substantial cross-resistance from enzalutamide to abiraterone, while enzalutamide retains activity post-abiraterone. The resulting longer time to second progression with abiraterone→enzalutamide sequencing (19.3 versus 15.2 months, HR 0.66) demonstrates that sequencing order materially affects cumulative treatment benefit, even when individual agents show similar first-line activity.

Combination Strategy Failures
The failure of enzalutamide plus abiraterone combination to improve outcomes compared to enzalutamide alone (median OS 32.7 versus 33.6 months, p=0.53) suggests overlapping mechanisms of action rather than complementary effects. The combination increased toxicity (grade 3-5 events 68.8% versus 55.6%) and treatment discontinuations (12% versus 5%) without survival benefit, indicating that concurrent dual AR pathway blockade offers no advantage over sequential monotherapy and imposes additional burden.

Similarly, adding enzalutamide to abiraterone in nonmetastatic disease showed no incremental benefit for metastasis-free survival beyond abiraterone alone, further supporting that these agents operate through sufficiently similar pathways that combination provides diminishing returns.

Methodological Considerations
The discrepancies between indirect comparisons and direct evidence warrant attention. While indirect meta-analysis suggested enzalutamide superiority for PFS endpoints, these comparisons relied on cross-trial assumptions that may not fully account for population differences. The authors acknowledged low evidence quality and explicitly called for direct comparison trials. Observational studies in the meta-analyses introduced potential confounding from treatment selection biases, as clinicians may preferentially assign certain agents based on patient characteristics not captured in adjusted analyses.

Toxicity-Driven Selection
The safety profiles, while broadly similar, show specific differences that should inform individualized treatment selection. Enzalutamide’s consistent ranking as most toxic for hypertension across disease settings and higher fatigue rates may be clinically meaningful for patients with cardiovascular comorbidities or functional impairment. Conversely, abiraterone requires corticosteroid coadministration and shows higher rates of hepatotoxicity, potentially complicating management in patients with diabetes or liver disease.

Based on this synthesis, enzalutamide appears to offer modest PFS advantages over abiraterone in CRPC, particularly for biochemical and radiographic endpoints, without clear overall survival benefit. In hormone-sensitive disease, both agents show similar efficacy in most contexts, with potential enzalutamide advantage in low-volume settings. Sequencing from abiraterone to enzalutamide preserves more treatment options than the reverse order. Given similar overall efficacy and survival outcomes, treatment selection should weigh disease volume, prior therapies, sequencing strategy, toxicity profiles, and patient-specific factors including cardiovascular risk, concomitant medications, and functional status.