Molecular profiling of peripheral blood is associated with circulating tumor cells content and poor survival in metastatic castration-resistant prostate cancer

Abstract

The enumeration of circulating tumor cells (CTCs) in peripheral blood correlates with clinical outcome in castration-resistant prostate cancer (CRPC). We analyzed the molecular profiling of peripheral blood from 43 metastatic CRPC patients with known CTC content in order to identify genes that may be related to prostate cancer progression. Global gene expression analysis identified the differential expression of 282 genes between samples with ≥5 CTCs vs <5 CTCs, 58.6% of which were previously described as over-expressed in prostate cancer (18.9% in primary tumors and 56.1% in metastasis). Those genes were involved in survival functions such as metabolism, signal transduction, gene expression, cell growth, death, and movement. The expression of selected genes was evaluated by quantitative RT-PCR. This analysis revealed a two-gene model (SELENBP1 and MMP9) with a high significant prognostic ability (HR 6; 95% CI 2.61 - 13.79; P<0.0001). The combination of the two-gene signature plus the CTCs count showed a higher prognostic ability than CTCs enumeration or gene expression alone (P<0.05). This study shows a gene expression profile in PBMNC associated with CTCs count and clinical outcome in metastatic CRPC, describing genes and pathways potentially associated with CRPC progression.

Keywords: cell search system; circulating tumor cells; microarrays; peripheral blood.

Figure 1. Survival analysis according to CTC count

A) Kaplan-Meier curves that estimate the probabilities of overall survival (OS) of CRPC patients with <5 and ≥5 CTCs. The log-rank test was used to assess the statistical difference between the two groups (P<0.001); B) Receiver operating characteristic (ROC) curve for prediction accuracy of ≥5 CTCs content in OS of CRPC.

Figure 2. Correlation between gene expression data in PBMNC and CTC count

A) Unsupervised clustering grouping patients according to gene expression data; B) Principal component analysis. The Y-axis represents the log2 of the CTC number plus one, and the X-axis is PC1 (Spearman correlation P<0.001).

Figure 3. Heatmap representing expression profile of the 50 most differentially expressed genes in samples from castration-resistant prostate cancer patients with ≥5 CTCs compared to those with <5 CTCs (FDR<0.001)

Rows represent genes and columns represent hybridized samples. Red pixels: upregulated genes; Green pixels: downregulated genes. The intensity of each color denotes the standardized ratio between each value and the average expression of each gene across all samples.

Figure 4. Survival analysis according to SELENBP1 and MMP9expression

A) Kaplan-Meier curves in patients with known CTCs count (N=43); B) Kaplan-Meier curves in the whole series of patients (N=70).

Figure 5. Receiver operating characteristic (ROC) curves illustrating CTCs count and two-gene signature (MMP9+SELENBP1) alone and combined for the prediction of OS