Effect of Prior Local Therapy on Response to First-line Androgen Receptor Axis Targeted Therapy in Metastatic Castrate-resistant Prostate Cancer: A Secondary Analysis of the COU-AA-302 Trial

Dual-Tracer 18 F-FDG and 68 Ga-PSMA PET/CT Imaging of Heterogeneous Phenotypes of Metastatic Castration-Resistant Prostate Cancer for Predicting Response to Novel Hormone Therapy

PURPOSE

This study evaluated interlesion heterogeneity in prostate cancer using dual-tracer imaging (PSMA and FDG) and explored its predictive value for novel hormone therapy (NHT).

PATIENTS AND METHODS

A total of 205 prostate cancer patients (23 biochemical recurrences, 68 metastatic castration-sensitive prostate cancers, 114 metastatic castration-resistant prostate cancers [mCRPC]) who underwent dual 18 F-FDG and 68 Ga-PSMA PET/CT imaging were retrospectively analyzed. Among them, 62 mCRPC patients received NHT. Patients were classified into 3 groups: PSMA+FDG-, PSMA+FDG+, and PSMA-FDG+. SUV ratio , the ratio of PSMA-SUV max to FDG-SUV max , was evaluated for its predictive value on progression-free survival (PFS).

RESULTS

The proportion of PSMA+FDG- patients decreased from biochemical recurrence to mCRPC stages, whereas FDG+ cases increased significantly ( P = 0.001). In the NHT cohort, group 3 (PSMA-FDG+) had significantly shorter median PFS than group 1 (133 vs 497 days; P = 0.027). In group 2, patients with a high SUV ratio had better median PFS than those with a low SUV ratio (368 vs 147 days; P = 0.031).

CONCLUSIONS

Dual-tracer imaging reveals interlesion heterogeneity in prostate cancer, and SUV ratio may help predict early response to NHT.

Prior Local Therapy and First-Line Apalutamide in Patients With Nonmetastatic Castration-Resistant Prostate Cancer: A Secondary Analysis of the SPARTAN Randomized Clinical Trial

Importance

Preclinical studies suggest that exposure to prostate-directed local therapy (LT) may influence the efficacy of subsequent systemic therapy including androgen receptor pathway inhibitors. However, there is insufficient clinical evidence to support this premise in patients with nonmetastatic castrate-resistant prostate cancer (nmCRPC).

Objective

To determine whether exposure to prior prostate-directed LT (radical prostatectomy [RP], radiation therapy [RT], or both) played any effect-modifying role in the treatment effect of apalutamide on metastasis-free survival (MFS) and overall survival (OS) in patients with nmCRPC.

Design, Setting, and Participants

This post hoc secondary analysis used individual patient data from SPARTAN (Study of Apalutamide [ARN-509] in Men With Non-Metastatic Castration-Resistant Prostate Cancer), a phase 3, double-blinded, placebo-controlled randomized clinical trial conducted at 332 sites in 26 countries. Between October 14, 2013, and December 15, 2016, patients with nmCRPC and a prostate-specific antigen doubling time of 10 months or less were randomly assigned to apalutamide vs placebo; all patients received androgen deprivation therapy. The final data analysis was performed on December 31, 2023.

Exposure

Prior prostate-directed LT.

Main Outcomes and Measures

Separate Cox proportional hazards regression models were constructed for OS and MFS, which included prior LT, treatment group, and an interaction term, in addition to a minimally sufficient set of confounders. Adjusted hazard ratios (HRs) with 95% CIs for MFS and OS were determined for the apalutamide groups with or without prior LT.

Results

Among the 1179 evaluable patients included in this analysis, 795 received prior LT and 384 did not. The median age of patients with and without prior LT was 70 (IQR, 45-90) years and 75 (IQR, 50-95) years, respectively. The median follow-up was 52.0 (IQR, 51.5-52.8) months. A differential treatment effect of apalutamide on MFS was observed between patients with and without prior LT (P for interaction = .009), with greater benefits for those with prior LT (adjusted HR, 0.22 [95% CI, 0.17-0.27]) compared with those without prior LT (adjusted HR, 0.35 [95% CI, 0.25-0.51]). However, there was insufficient evidence of a differential treatment effect on OS among subgroups stratified by exposure to prior LT (P for interaction = .23), with improved OS in the subgroup with prior LT (adjusted HR, 0.72 [95% CI, 0.57-0.92]) but no significant difference in OS in the subgroup without prior LT (adjusted HR, 0.92 [95% CI, 0.64-1.31]).

Conclusions and Relevance

This post hoc analysis of the SPARTAN trial provides evidence of an interaction between prior LT and apalutamide in patients with nmCRPC, with a clinically significant and more favorable treatment effect from apalutamide on MFS among patients with prior LT. Further studies are needed to validate these findings.

Trial Registration

ClinicalTrials.gov Identifier: NCT01946204.

Overall Survival and Cancer-Specific Mortality in Patients with Prostate Cancer Undergoing Definitive Therapies: A Narrative Review

The overall survival (OS) of patients with prostate cancer (PCa) who receive locally definitive therapy is generally better than that of patients who do not receive definitive therapy. There is no difference in the incidence of local recurrence or distant metastasis between treatment modalities. Because the prognosis of PCa is relatively good, many studies have focused on quality of life after treatment as an endpoint. However, a limited number of patients develop biochemical recurrence after definitive treatment for PCa and subsequently develop distant metastasis or die from PCa. Therefore, we believe that preventing local recurrence and distant metastasis and prolonging the OS should be emphasized when selecting a treatment modality for PCa. In this review, the significance and usefulness of radical prostatectomy and radiation therapy as the main modalities of definitive therapies for local PCa and locally advanced PCa were evaluated, as well as the outcomes of OS and PCa-specific mortality and the treatment options after biochemical recurrence to improve the oncological outcomes.