Chemokine markers predict biochemical recurrence of prostate cancer following prostatectomy

Abstract

Purpose: Stratifying patients who have a high risk of prostate cancer recurrence following prostatectomy can potentiate the use of adjuvant therapy at an early stage. Inflammation has emerged as a mediator of prostate cancer metastatic progression. We hypothesized that chemokines can be biomarkers for distinguishing patients with high risk for biochemical recurrence of prostate cancer.

Experimental design: In a nested case-control study, 82 subjects developed biochemical recurrence within 5 years of prostatectomy. Prostate tissues from 98 age-matched subjects who were recurrence-free following prostatectomy in the same period were the controls. A high-throughput lectin-based enrichment of prostate tissue enabled multiplex ELISA to identify the expression of three chemokines to discriminate the two patient populations.

Results: The expression of CX3CL1 and IL-15 in prostate tissue was associated with 5-year biochemical recurrence-free survival following prostatectomy. However, the expression of chemokine ligand 4 (CCL4) was associated with biochemical recurrence. Multivariable logistic regression model combining preoperative prostate-specific antigen, Gleason score, surgical margin, and seminal vesicle status with the three chemokines doubled the specificity of prediction at 90% sensitivity compared with use of the clinicopathologic variables alone (P < 0.0001). Survival analysis yielded a nomogram that supported the use of CX3CL1, IL-15, and CCL4 in predicting 1-, 3-, and 5-year recurrence-free survival after prostatectomy.

Conclusions: Each of the three chemokines can serve as independent predictors of biochemical recurrence. However, the combination of chemokine biomarkers plus clinicopathologic variables discriminated prostatectomy subjects for the probability of biochemical recurrence significantly better than clinicopathologic variables alone.

Figure 1. The histologic evaluation of the frozen prostate cores

(A) Each tissue core was cut longitudinally into thirds for duplicate chemokine enrichment and histology analysis, respectively. Subjects B and C developed biochemical recurrence, but subject D was free of recurrence for the five years following prostatectomy.

Figure 2. Receiver Operating Characteristics (ROC) curves for the prediction models impacted by chemokines (CCL4, CX3CL1, IL-15)

Predicted probability of recurrence for each subject was computed from logistic regression models including pre-operative PSA, surgical margin status, seminal vesicle invasion status, pathologic Gleason score, with and without chemokines. Specificity and sensitivity were computed at each possible cutoff on the predicted probability for the two models. The area under the curve (AUC) were compared for the two models.

Figure 3. The Kaplan-Meier estimates of the recurrence-free survival based on chemokine expression

The patients were separated into two groups, divided at median tissue level for CCL4 (A), CX3CL1 (B), and IL-15 (C). The two groups were discriminated by the median respective chemokine expression concentration indicated, termed upper half, those below the median lower half. The recurrence-free survival probabilities were estimated by the Kaplan-Meier method and the differences tested using the log-rank test. Each of the dichotomous chemokine expression levels supported statistically significant differences in biochemical recurrence free survival.

Figure 4. Cox proportional hazard regression

Multivariable Cox proportional hazard regression for biochemical recurrence-free survival demonstrated that preoperative PSA, surgical margin, CCL4 and CX3CL1 were significant predictors of recurrence-free survival. For each predictor variable, the vertical bars illustrate the hazard ratio estimate and the gray horizontal bars represent the respective 95% confidence intervals described in Table 3. The hazard ratios were computed for a change from the lower quartile to upper quartile in continuous variables, namely Gleason Score: 6 – 8, Preoperative PSA: 5 – 9, CCL4: 0.003 to 0.04, CX3CL1: 0.01 to 0.07, IL15: 0.004 to 0.06. For both surgical margins and seminal vesicle involvement, negative is the reference group.

Figure 5. Nomogram from the Cox proportional hazard regression model

The Cox proportional hazard regression model was used to create a prediction model for 1-, 3- and 5- year recurrent-free survival. A value in each predictor variable corresponds to a point scale (top). The sum of the individual predictor variable points correspond to the probability of 1-, 3-, and 5-year recurrent-free survival (bottom).