Expression profiling of cancerous and normal breast tissues identifies microRNAs that are differentially expressed in serum from patients with (metastatic) breast cancer and healthy volunteers

Eleni van Schooneveld, Maartje Ca Wouters, Ilse Van der Auwera, Dieter J Peeters, Hans Wildiers, Peter A Van Dam, Ignace Vergote, Peter B Vermeulen, Luc Y Dirix, Steven J Van Laere, Eleni van Schooneveld, Maartje Ca Wouters, Ilse Van der Auwera, Dieter J Peeters, Hans Wildiers, Peter A Van Dam, Ignace Vergote, Peter B Vermeulen, Luc Y Dirix, Steven J Van Laere

Abstract

Introduction: MicroRNAs (miRNAs) are a group of small noncoding RNAs involved in the regulation of gene expression. As such, they regulate a large number of cellular pathways, and deregulation or altered expression of miRNAs is associated with tumorigenesis. In the current study, we evaluated the feasibility and clinical utility of circulating miRNAs as biomarkers for the detection and staging of breast cancer.

Methods: miRNAs were extracted from a set of 84 tissue samples from patients with breast cancer and eight normal tissue samples obtained after breast-reductive surgery. After reverse transcription and preamplification, 768 miRNAs were profiled by using the TaqMan low-density arrays. After data normalization, unsupervised hierarchical cluster analysis (UHCA) was used to investigate global differences in miRNA expression between cancerous and normal samples. With fold-change analysis, the most discriminating miRNAs between both tissue types were selected, and their expression was analyzed on serum samples from 20 healthy volunteers and 75 patients with breast cancer, including 16 patients with untreated metastatic breast cancer. miRNAs were extracted from 200 μl of serum, reverse transcribed, and analyzed in duplicate by using polymerase chain reaction (qRT-PCR).

Results: UHCA showed major differences in miRNA expression between tissue samples from patients with breast cancer and tissue samples from breast-reductive surgery (P < 0.0001). Generally, miRNA expression in cancerous samples tends to be repressed when compared with miRNA expression in healthy controls (P = 0.0685). The four most discriminating miRNAs by fold-change (miR-215, miR-299-5p, miR-411, and miR-452) were selected for further analysis on serum samples. All miRNAs at least tended to be differentially expressed between serum samples from patients with cancer and serum samples from healthy controls (miR-215, P = 0.094; miR-299-5P, P = 0.019; miR-411, P = 0.002; and miR-452, P = 0.092). For all these miRNAs, except for miR-452, the greatest difference in expression was observed between serum samples from healthy volunteers and serum samples from untreated patients with metastatic breast cancer.

Conclusions: Our study provides a basis for the establishment of miRNAs as biomarkers for the detection and eventually staging of breast cancer through blood-borne testing. We identified and tested a set of putative biomarkers of breast cancer and demonstrated that altered levels of these miRNAs in serum from patients with breast cancer are particularly associated with the presence of metastatic disease.

Figures

Figure 1
Figure 1
The distribution of polymerase chain reaction (PCR) efficiencies, calculated as the differences between the Ct values of undiluted sample and the Ct values of a 10-fold diluted sample. (A) Theoretically, this difference should equal 3.32 or 2log(10). All miRNA assays with a difference in Ct value between 3.32% and 25% were included for further analysis. A blue dashed line indicates the boundaries of the interval; a blue solid line indicates the theoretical expected value of 3.32. To account for differences in preamplification, we compared the Ct values of a sample before and after preamplification. The median difference in Ct value was 8, and all miRNA assays with a difference of 8% ± 25% were included for further analysis. The scatterplot in (B) demonstrates an almost perfect linear relation for those selected miRNAs before and after preamplification. The blue line represents the regression line, for which the equation is given on top of the scatterplot. To evaluate assay reproducibility, we tested four samples in duplicate. The scatterplot in (C) demonstrates the result for one of these samples. The blue line represents the regression line, and the correlation coefficient resulting from the comparison of both profiles is given on top of the scatterplot. Further technical validation of our miRNA-expression data was performed for 12 samples by analyzing their miRNA-expression profile with the nCounter Analysis System and comparing this result with the qRT-PCR-based miRNA-expression profile. The scatterplot in (D) demonstrates the result for one of these samples. The blue line represents the regression line, and the correlation coefficient resulting from the comparison of both profiles is given on top of the scatterplot.
Figure 2
Figure 2
Heatmap showing the result of an UHCA (Manhattan distance, Ward linkage) for all 373 miRNAs in all 92 samples. The miRNA-expression data are represented in matrix format, with rows indicating miRNAs and columns indicating samples. Overexpressed miRNAs are color-coded red, and repressed miRNAs are color-coded green. Color saturation indicates the level of overexpression. Six samples clusters could be discerned based on miRNA-expression differences, indicated by alternating blue and grey colors in the dendrogram. Underneath the sample dendrogram, the molecular-subtype classification is indicated (red, Basal-like; orange, ErbB2+; green, Luminal A; blue, Luminal B; gray, Normal-like). The true-normal breast samples are indicated by a darker shade of gray. The colored bar to the side of the heatmap indicates the array card to which the corresponding assay is allocated (red, A; blue, B).
Figure 3
Figure 3
Comparison of the mRNA-based molecular subtype classification by using the SSP method with the miRNA-based classification by using the expression centroids reported by Blenkiron and colleagues. This analysis was performed only for those samples for which Affymetrix mRNA-expression profiles are available (N = 66). The SSP-classification is provided in the X-axis (B, Basal; E, ErbB2+; LA, Luminal A; LB, Luminal B; N, Normal-like; and R, Rest). The Spearman correlation coefficients resulting from the miRNA-based molecular subtype classification are indicated in the Y-axis. For each miRNA-based molecular subtype-specific centroid and each sample in our data set, the Spearman correlation coefficients were determined. The molecular subtype-specific correlation coefficients were statistically compared between samples belonging to and not belonging to the SSP-defined molecular subtype of interest. P values are indicated under the corresponding boxplots.
Figure 4
Figure 4
Comparison of normal breast samples with tumor samples. We identified 59 differentially expressed miRNAs between tumor samples and normal breast samples. The median expression of these miRNAs is significantly elevated in normal breast samples, as illustrated by the boxplot (A). The top four miRNAs (miR-215, miR-299-5p, miR-411, and miR-452) with the greatest difference between normal breast samples and breast tumor samples by fold change are depicted in panels B through E. The corresponding false discovery rate is provided in top of each boxplot. All miRNAs are significantly overexpressed in normal breast samples.
Figure 5
Figure 5
Comparison of the expression profiles of miR-215, miR-299-5p, miR-411, and miR-452 between serum samples from patients with breast cancer and serum samples from healthy volunteers (A through D). The boxplots on panels E through H represent the comparison of the expression profiles of the same miRNAs between serum samples from healthy volunteers and from patients with metastatic breast cancer receiving and not receiving treatment. The P values indicating the significance of the difference are indicated on top of the boxplots.

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