Intra-tumor heterogeneity of microRNA-92a, microRNA-375 and microRNA-424 in colorectal cancer

• We assess intra-tumor and inter-patient variation of miRNA expression in CRC tissue.
• We find intra-tumor variances constituting 30% of the total variance.
• We demonstrate possible functional miRNA deregulations between tumor zones.
• Specific tissue sampling is crucial for correct interpretation of molecular analyses.

Various microRNAs (miRNAs) have been investigated in order to improve diagnostics and risk assessment in colorectal cancer (CRC). To clarify the potential of miRNA profiling in CRC, knowledge of intra-tumor heterogeneity in expression levels is crucial.The study aim was to estimate the intra-tumor variance of three selected miRNAs: miR-92a, miR-375 and miR-424 in CRC tissue.Material and methodsA retrospective study on archived formalin-fixed paraffin embedded tissue from 9 patients with CRC. miRNA tissue expression levels were analyzed by qRT-PCR on tissue representing luminal, central and invasive border zones. Variance components were estimated based on ∆∆Cp values using mixed modeling and presented as coefficients of variation (CV).ResultsIntra-tumor variance was approximately half of the variance observed between patients with a mean intra-tumor CV of 56.4% (range 33.1–77.1%) and a mean inter-patient CV of 101.7% (range 48.8–152.7%). Furthermore we found a significant systematic difference in expression levels between tumor zones for miR-92a and miR-375 with a luminal-invasive difference equal to 0.60 Cp (95% CI: 0.30–0.89, p = 0.0003) for miR-92a and a luminal-invasive difference equal to 0.78 Cp (95% CI: 0.10–1.46, p = 0.027) for miR-375. ConclusionWhile the intra-tumor variance of miR-92a, miR-375 and miR-424 is substantial, it only constitutes approximately 30% of the total variation. Functional deregulation between tumor zones might contribute to variations in measured expression levels, and thus knowledge of specific intra-tumor expression patterns is crucial in tissue sampling for research as well as in future diagnostics.