Prostate-Specific Ets (PSE) factor: a novel marker for detection of metastatic breast cancer in axillary lymph nodes

Abstract

Prostate Specific Ets factor is a recently identified transcriptional activator that is overexpressed in prostate cancer. To determine whether this gene is overexpressed in breast cancer, we performed a virtual Northern blot using data available online at the Cancer Genome Anatomy Project website. Ninety-five SAGE libraries were probed with a unique sequence tag to the Prostate Specific Ets gene. The results indicate that Prostate Specific Ets is expressed in 14 out of 15 breast cancer libraries (93%), nine out of 10 prostate cancer libraries (90%), three out of 40 libraries from other cancers (7.5%), and four out of 30 normal tissue libraries (13%). To determine the possibility that the Prostate Specific Ets gene is a novel marker for detection of metastatic breast cancer in axillary lymph nodes, quantitative real-time RT-PCR analyses were performed. The mean level of Prostate Specific Ets expression in lymph nodes containing metastatic breast cancer (n=22) was 410-fold higher than in normal lymph node (n=51). A receiver operator characteristic curve analysis indicated that Prostate Specific Ets was overexpressed in 18 out of 22 lymph nodes containing metastatic breast cancer (82%). The receiver operator characteristic curve analysis also indicated that the diagnostic accuracy of the Prostate Specific Ets gene for detection of metastatic breast cancer in axillary lymph nodes was 0.949. These results provide evidence that Prostate Specific Ets is a potentially informative novel marker for detection of metastatic breast cancer in axillary lymph nodes, and should be included in any study that involves molecular profiling of breast cancer.

Copyright 2002 Cancer Research UK

Figures

Figure 1

Genomic structure of the PSE gene. Intron/exon boundaries of the PSE gene were obtained as described in Materials and Methods. The nucleotide lengths of exons 1–6 are: 1 (386), 2 (465), 3 (198), 4 (48), 5 (146), 6 (650). Lengths (in nucleotides) of introns following respective exons are: 1 (11 444), 2 (2338), 3 (1421), 4 (118), and 5 (797). Functional domains of the exons (Oettgen et al, 2000) are indicated in the top portion of the boxes. Translation start site is indicated by arrow at far left of exon 2. Arrow at the top right of exon 2 indicates approximate position of forward primer used for real-time RT–PCR analyses is indicated, while arrow below exon 3 indicates position of the reverse primer.

Figure 2

Expression of PSE in cancer cell lines, breast tissue, and lymph nodes. Real-time PCR analyses were performed using primers to the PSE gene and various cell line or tissue samples described in Materials and Methods. Ct values for each gene were determined from triplicate reactions. ΔCt values were obtained by subtracting the mean Ct value of β2- microglobin for the respective sample from the mean Ct value for PSE. Symbols for the cell lines are: Pancreas: triangle, Panc1; open square, Capan1. Prostate: open square, DUI145; X, LnCap; triangle, PC3. Breast: open circle, MDA453; open square, MDA231; −, MDA361; triangle, SkBr3; X, MCF7; +, MCF10A. Number of samples analysed for each tissue: 51 negative control normal lymph nodes (solid circles=females, open triangles=males), 22 pathology-positive axillary lymph nodes (open square) and 22 pathology-negative axillary lymph nodes (open diamond). Horizontal line indicates ΔCt threshold value obtained at a 98% specificity level using the ROC curve analysis described in the text.