• Cancer
• colorectal cancer screening
• molecular oncology
• RNA expression
• tumour markers

We read with interest the recent article by Ng et al which concludes that plasma microRNAs (miRNAs) hold potential as non-invasive screening tools for colorectal cancer (CRC).1 Investigation of miRNAs in the circulation has recently gained momentum, upon recognising their potential as novel tumour markers.2 In our institution we have recently identified that circulating miR-195 and let-7a are significantly elevated in blood from patients with breast cancer (n=83) compared with controls (n=44). Similar to Ng and colleagues, we observed a postoperative decrease in systemic miRNA levels, and a significant correlation between systemic and tumour miRNA levels, and stage of disease.3 Whilst we agree with Ng et al that plasma miRNAs may be useful CRC biomarkers, we have several comments in relation to their article.

First, the use of plasma above serum or whole blood is questionable. There is as yet …