External validation and newly development of a nomogram to predict overall survival of abiraterone-treated, castration-resistant patients with metastatic prostate cancer

Abstract

Abiraterone acetate is approved for the treatment of castration-resistant prostate cancer (CRPC); however, its effects vary. An accurate prediction model to identify patient groups that will benefit from abiraterone treatment is therefore urgently required. The Chi model exhibits a good profile for risk classification, although its utility for the chemotherapy-naive group is unclear. This study aimed to externally validate the Chi model and develop a new nomogram to predict overall survival (OS). We retrospectively analyzed a cohort of 110 patients. Patients were distributed among good-, intermediate-, and poor-risk groups, according to the Chi model. The good-, intermediate-, and poor-risk groups had a sample size of 59 (53.6%), 34 (30.9%), and 17 (15.5%) in our dataset, and a median OS of 48.4, 29.1, and 10.5 months, respectively. The C-index of external validation of Chi model was 0.726. Univariate and multivariate analyses identified low hemoglobin concentrations (<110 g l^-1), liver metastasis, and a short time interval from androgen deprivation therapy to abiraterone initiation (<36 months) as predictors of OS. Accordingly, a new nomogram was developed with a C-index equal to 0.757 (95% CI, 0.678-0.836). In conclusion, the Chi model predicted the prognosis of abiraterone-treated, chemotherapy-naive patients with mCRPC, and we developed a new nomogram to predict the overall survival of this group of patients with less parameters.

Keywords: abiraterone acetate; castration-resistant prostate cancer; external validation; nomogram; survival.

Figure 1

The OS and number of patients of each risk factor according to Chi model. OS: overall survival; ECOG: Eastern Cooperative Oncology Group; ALP: alkaline phosphatase (IU l^-1); ALB: albumin (g l^-1); LDH: lactate dehydrogenase (IU l^-1). *Time interval from androgen deprivation therapy to abiraterone initiation (month).

Figure 2

Overall survival curves according to Chi prognostic model.

Figure 3

Overall survival nomogram. *Time interval from androgen deprivation therapy to abiraterone initiation. OS: overall survival. It needs two steps to get the 1- and 2-year overall survival probability from the nomogram above: (I) draw a line straight up to the “points” axis from the value (e.g., for hemoglobin the values are “<110g/L” and “≤110g/L”) of each risk factor (hemoglobin, liver metastasis and time from ADT to abiraterone initiation). (II) Add the point scores of each risk factor and locate the total score on the axis of “total points”. Then draw a vertical line from the total score down to the 1- or 2-year overall survival probability axes to obtain the probability.