Clinical outcomes in chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC) patients (pts) treated with abiraterone acetate (ABI) stratified by prognosis

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Background: Pts with mCRPC can have very disparate outcomes. A prognostic index was developed from the COU-AA-301 trial in post-chemotherapy mCRPC pts treated with ABI (J Clin Oncol 31, 2013 (suppl; abstr 5013)). The model included 6 risk-factors (RF) associated with poor outcome: ECOG performance status (PS) ⩾2, presence of liver metastases, time from start of LHRH agonists/antagonists to start of ABI ⩽36 months, albumin ⩽40 g/L, alkaline phosphatase (ALP) ⩾ upper limit of normal (ULN) and lactate dehydrogenase (LDH) ⩾ULN. The aim of this study was to evaluate this model in an unselected, sequentially treated, population-based cohort of chemotherapy-naïve mCRPC patients treated with ABI.

Materials and Methods: We identified 246 chemotherapy-naïve mCRPC patients treated with ABI between July 2009 and February 2015 at six British Columbia Cancer Agency centres. Patient records missing information on one of the six RFs were excluded. 197 patients were classified into good (0–1 RFs), intermediate (2–3 RFs) and poor (4–6 RFs) prognostic (prog) groups according to the COU-AA-301 model. PSA response rates (PSA decline ⩾50% confirmed ⩾3 weeks later), time to PSA progression (PCWG2 criteria) and OS data were collected. Univariate analysis examining association between baseline factors and survival outcomes was performed using Cox proportional hazards regression. Factors significant on univariate analysis were incorporated into a multivariate model for OS.

Results: 31%, 52% and 17% of pts were classified as good, intermediate and poor risk respectively. PSA response, time to PSA progression and OS outcome significantly differed between prog group (Table). Compared to good prog pts, the HR (95% CI) for OS in intermediate and poor prog pts was 2.68 (1.60–4.47, p < 0.001; log-rank) and 6.53 (3.56–11.95, p < 0.001; log-rank). On multivariate analysis, ECOG PS (HR 2.5, p < 0.001), visceral metastases (HR 2.2, p = 0.03) and ALP (HR 2.2, p = 0.001) were confirmed as independent risk factors for decreased OS.

Conclusion: The present analysis confirms that the prognostic index derived from the COU-301 study also prognostically discriminates chemotherapy-naïve patients receiving ABI. Patients with intermediate and poor prognosis also had a lower PSA response rate and shorter time to progression. Identifying patients at risk of poor outcomes is important for informing clinical practice and clinical trial designs.

Median time to PSA progression [months] (0–1 RF)N IntermediateM (4–6 RF) <0.001** (log rank)
  Prognostic group p-value  
  Good (0–1 RF) Intermediate (2–3 RF) Poor (4–6 RF)  
PSA response [%] 55 38 39 0.03* (chi-square)
Median time to PSA progression [months] 9.1 6.6 5.6 0.04** (log-rank)
Median OS [months] 29.4 13.8 8.7 <0.001** (log rank)

*Good vs. intermediate/poor prognosis patients.**Good vs. intermediate vs. poor prognosis patients.

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