In situ measurement of miR-205 in malignant melanoma tissue supports its role as a tumor suppressor microRNA.

Oncogenic and tumor suppressing microRNAs (miRNAs) have emerged as key regulators of gene expression in many types of cancer including melanoma. We utilized quantitative in situ hybridization (qISH) to evaluate the tumor suppressing properties of miRNA, miR-205 in a population of human tumors. We hypothesize decreased miR-205 would be associated with more aggressive tumors. Multiplexing miR-205 qISH with immunofluorescent assessment of S100/GP100 allowed us to quantitatively evaluate miR-205 expression using the AQUA method of quantitative immunofluorescence. The specificity of the assay was validated using blocking oligos and transfected cell lines as controls. Outcomes were assessed on the Yale Melanoma Discovery Cohort consisting of 105 primary melanoma specimens and validated on an independent set of 206 primary melanomas (Yale Melanoma Validation Cohort). Measurement of melanoma cell miR-205 levels shows a significantly shorter melanoma-specific survival in patients with low expression. Multivariate analysis shows miR-205 levels are significantly independent of stage, age, gender, and Breslow depth. Low levels of melanoma cell miR-205 expression as quantified by ISH show worse outcome, supporting the role of miR-205 as a tumor suppressor miRNA. The quantification of miR-205 in situ suggests potential for the use of miRNAs in future prognostic or predictive models.