It is crucial to have true cancer-specific biomarkers for early cancer detection as well as for minimal residual disease monitoring, which has been extensively demonstrated in hematologic maligancies (43) . Such biomarkers could help to avoid under-or over-treatment. Thus, there is past interest (24, 44) in applying TMPRSS2:ERG fusion assays for such application since PSA and many other markers in development are not truly prostate cancer-specific (45) . A recent study reported a TMPRSS2:ERG assay with a sensitivity of detecting 1600 VCaP cells (24) . However, this level of sensitivity might not be sufficient for broad clinical application, especially with small biopsy specimens or urine samples. We were able to achieve an assay sensitivity of 532 pg of total RNA derived from VCaP cells, an equivalent to 1-3 cells (Figure 2 ). Because our assay is simple and amenable to automation, it is readily adaptable to clinical studies. While it has been challenging to adapt microarray-based technology to the clinic, some tests (e.g. AmpliChip CYP450 and MammaPrint) have been approved by FDA (46) .