Noninvasive detection of TMPRSS2:ERG fusion transcripts in the urine of men with prostate cancer

Abstract

We recently reported the identification of recurrent gene fusions in the majority of prostate cancers involving the 5' untranslated region of the androgen-regulated gene TMPRSS2 and the ETS family members ERG, ETV1, and ETV4. Here we report the noninvasive detection of these gene fusions in the urine of patients with clinically localized prostate cancer. By quantitative polymerase chain reaction, we assessed the expression of ERG and TMPRSS2:ERG transcripts in urine samples obtained after prostatic massage from 19 patients (11 prebiopsy and 8 pre-radical prostatectomy) with prostate cancer. We observed a strong concordance between ERG overexpression and TMPRSS2:ERG expression, with 8 of 19 (42%) patients having detectable TMPRSS2:ERG transcripts in their urine. Importantly, by fluorescence in situ hybridization, we confirmed the presence or the absence of TMPRSS2:ERG gene fusions in matched prostate cancer tissue samples from three of three patients with fusion transcripts in their urine and from two of two patients without fusion transcripts in their urine. These results demonstrate that TMPRSS2:ERG gene fusions can be detected in the urine of patients with prostate cancer and support larger studies on prospective cohorts for noninvasive detection of prostate cancer.

Figure 1

Detection of ERG and ETV1 transcripts in urine spiked with prostate cancer cell lines. The indicated number of LNCaP (red bar: high ETV1 expression) or VCaP (blue bar: high ERG and TMPRSS2:ERG expression) prostate cancer cells was spiked into 1 ml of urine. Approximately 1.6 million cells of each cell line were used without being spiked (Direct). Total RNA was isolated and reverse-transcribed to cDNA before qPCR analysis. The relative amount of ERG and ETV1 for each sample was normalized to the amount of GAPDH.

Figure 2

Confirmation of the presence or the absence of TMPRSS2:ERG detection in the urine using FISH on matched tissue sections. Matched prostate cancer tissue samples for five samples were assessed by FISH for TMPRSS2:ERG fusion using a split-probe assay for ERG rearrangement (Table 1). Hematoxylin and eosin staining (A and B) and representative FISH images (C and D) for samples 5778 and 5790 are shown. A negative FISH assay (C) for sample 5778 is indicated by two pairs of colocalized red and green signals (yellow arrows) per cell, whereas a positive FISH assay is indicated by one pair of split red and green signals (not shown) or exclusive loss of the 5′ ERG probe (red signal) resulting in one pair of colocalized signals (yellow arrows) and one green signal (green arrows) per cell (D), as shown for sample 5790.