Predictive value of Sp1/Sp3/FLIP signature for prostate cancer recurrence

Abstract

Prediction of prostate cancer prognosis is challenging and predictive biomarkers of recurrence remain elusive. Although prostate specific antigen (PSA) has high sensitivity (90%) at a PSA level of 4.0 ng/mL, its low specificity leads to many false positive results and considerable overtreatment of patients and its performance at lower ranges is poor. Given the histopathological and molecular heterogeneity of prostate cancer, we propose that a panel of markers will be a better tool than a single marker. We tested a panel of markers composed of the anti-apoptotic protein FLIP and its transcriptional regulators Sp1 and Sp3 using prostate tissues from 64 patients with recurrent and non-recurrent cancer who underwent radical prostatectomy as primary treatment for prostate cancer and were followed with PSA measurements for at least 5 years. Immunohistochemical staining for Sp1, Sp3, and FLIP was performed on these tissues and scored based on the proportion and intensity of staining. The predictive value of the FLIP/Sp1/Sp3 signature for clinical outcome (recurrence vs. non-recurrence) was explored with logistic regression, and combinations of FLIP/Sp1/Sp3 and Gleason score were analyzed with a stepwise (backward and forward) logistic model. The discrimination of the markers was identified by sensitivity-specificity analysis and the diagnostic value of FLIP/Sp1/Sp3 was determined using area under the curve (AUC) for receiver operator characteristic curves. The AUCs for FLIP, Sp1, Sp3, and Gleason score for predicting PSA failure and non-failure were 0.71, 0.66, 0.68, and 0.76, respectively. However, this increased to 0.93 when combined. Thus, the "biomarker signature" of FLIP/Sp1/Sp3 combined with Gleason score predicted disease recurrence and stratified patients who are likely to benefit from more aggressive treatment.

Figure 1. Box plots showing significant differences in mean total score for IHC of Sp1, Sp3, and FLIP between recurrent and non-recurrent cases as determined by Wilcoxon rank-sum test.

Figure 2. A. H&E staining and IHC analysis of expression of FLIP, Sp1, and Sp3 in a representative sample of non-recurrent PCA [Gleason 7 (3+4)] under low magnification (left) and high magnification (right).

The total score for this sample was 0, 6, and 0 for FLIP, Sp1, and Sp3 respectively. B. H&E and IHC staining of FLIP, Sp1 and Sp3 in a representative sample from a patient with recurrent PCA [(Gleason 9 (4+5)] under low magnification (left) and high magnification (right). The total score for this sample was 7, 8, and 6 for FLIP, Sp1, and Sp3, respectively.

Figure 3. Plot of sensitivity versus specificity.

Area under the ROC curves calculated for FLIP (0.71), Sp1 (0.66), Sp3 (0.68), and Gleason (0.76) show various degrees of discrimination as predictors of recurrence. An area under the ROC curve of 0.8 to 1.0 is considered to be very good to excellent discrimination, whereas 0.5 indicates no discrimination.

Figure 4. Plot of sensitivity versus specificity.

Area under the ROC curves calculated for combination of FLIP, Sp1, Sp3, Gleason score, and their interactions gives a value of 0.93 indicating excellent discrimination between non-recurrent and recurrent cases.

Figure 5. Plot of sensitivity versus specificity.

At a probability cut-off point of 0.45 both the sensitivity (80%) and specificity (85.3%) for this combination of markers is high, indicating excellent discrimination power of the combination.

Figure 6. A. Predicted probability of recurrence when Gleason is low grade 5–7(3+4) for different levels of Sp1 (0, 3, and 6) and Sp3 (0–6) as a function of FLIP (0–8) interaction.

Cases above the cut-off point of 0.45 (dashed line) are predicted to recur. The interaction of FLIP and Sp3 is shown as solid color lines on the X-axis. B. Predicted probability of recurrence when Gleason is high grade 7 (4+3) for different levels of Sp1 (0, 3, and 6) and Sp3 (0–6) as a function of FLIP (0–8) interaction. Cases above the cut-off point of 0.45 (dashed line) are predicted to recur. The interaction of FLIP and Sp3 is shown as solid color lines on the X-axis.