Abiraterone vs. docetaxel for metastatic hormone-sensitive prostate cancer: A microsimulation model

Cost-Effectiveness Analysis for Therapy Sequence in Advanced Cancer: A Microsimulation Approach with Application to Metastatic Prostate Cancer

PURPOSE

Patients with advanced cancer may undergo multiple lines of treatment, switching therapies as their disease progresses. We developed a general microsimulation framework to study therapy sequence and applied it to metastatic prostate cancer.

METHODS

We constructed a discrete-time state transition model to study 2 lines of therapy. Using digitized published survival curves (progression-free survival, time to progression, and overall survival [OS]), we inferred event types (progression or death) and estimated transition probabilities using cumulative incidence functions with competing risks. We incorporated within-patient dependence over time; first-line therapy response informed subsequent event probabilities. Parameters governing within-patient dependence calibrated the model-based results to a target clinical trial. We applied these methods to 2 therapy sequences for metastatic prostate cancer, wherein both docetaxel (DCT) and abiraterone acetate (AA) are appropriate for either first- or second-line treatment. We assessed costs and quality-adjusted life-years (5-y QALYs) for 2 treatment strategies: DCT → AA versus AA → DCT.

RESULTS

Models assuming within-patient independence overestimated OS time, which corrected with the calibration approach. With generic pricing, AA → DCT dominated DCT → AA, (higher 5-y QALYs and lower costs), consistent for all values of calibration parameters (including no correction). Model calibration increased the difference in 5-y QALYs between treatment strategies (0.07 uncorrected v. 0.15 with base-case correction). Applying the correction decreased the estimated difference in cost (-$5,360 uncorrected v. -$3,066 corrected). Results were strongly affected by the cost of AA. Under a lifetime horizon, AA → DCT was no longer dominant but still cost-effective (incremental cost-effectiveness ratio: $19,463).

CONCLUSIONS

We demonstrate a microsimulation approach to study the cost-effectiveness of therapy sequences for advanced prostate cancer, taking care to account for within-patient dependence.

HIGHLIGHTS

We developed a discrete-time state transition model for studying therapy sequence in advanced cancers.Results are sensitive to dependence within patients.A calibration approach can introduce dependence across lines of therapy and closely match simulation outcomes to target trial outcomes.

Population-Based Study of Docetaxel or Abiraterone Effectiveness and Predictive Markers of Progression Free Survival in Metastatic Castration-Sensitive Prostate Cancer

BACKGROUND

Both Docetaxel (DOC) and Abiraterone (ABI) improve the survival of men with metastatic, castration sensitive prostate cancer (mCSPC). However, the outcome among mCSPC patients is highly variable, while there is a lack of predictive markers of therapeutic benefit. Furthermore, there is limited data on the comparative real-world effectiveness of adding DOC or ABI to androgen deprivation therapy (ADT).

METHODS

We conducted a retrospective analysis of 121 mCSPC patients treated at Odette Cancer Centre (Toronto, ON, Canada) between Dec 2014 and Mar 2021 (DOC n = 79, ABI n = 42). The primary endpoint studied was progression free survival (PFS), defined as the interval from start of ADT to either (i) biochemical, radiological, or symptomatic progression, (ii) start of first-line systemic therapy for castration-resistant prostate cancer (CRPC), or (iii) death, whichever occurred first. To identify independent predictive factors for PFS in the entire cohort, a Cox proportional hazard model (stepwise selection) was applied. Overall survival (OS) was among secondary endpoints.

RESULTS

After a median follow-up of 39.6 and 25.1 months in the DOC and ABI cohorts, respectively, 79.7% of men in the DOC and 40.5% in the ABI group experienced a progression event. PFS favored the ABI cohort (p = 0.0038, log-rank test), with 78.0% (95%CI 66.4-91.8%) of ABI versus 67.1% (57.5-78.3%) of DOC patients being free of progression at 12 months. In univariate analysis superior PFS was significantly related to older age at diagnosis of mCSPC, metachronous metastatic presentation, low-volume (CHAARTED), and low-risk (LATITUDE) disease, ≥90% PSA decrease at 3 months (PSA90), and PSA nadir ≤0.2 at 6 months. Age (HR = 0.955), PSA90 (HR = 0.462), and LATITUDE risk stratification (HR = 1.965) remained significantly associated with PFS in multivariable analysis. OS at 12 months was 98.7% (96.3-100%) and 92.7% (85.0-100%) in the DOC and ABI groups (p = 0.97), respectively.

CONCLUSIONS

In this real-world group of men undergoing treatment intensification with DOC or ABI for mCSPC, we did not find a significant difference in OS, but PFS was favoring ABI. Age at diagnosis of mCSPC, PSA90 at 3 months and LATITUDE risk classification are predictive factors of PFS in men with mCSPC.