microRNa expression profiling in adrenal myelolipoma, adrenocortical carcinoma and adrenocortical adenoma

Background: Adrenal myelolipoma (AML) is a relatively common and invariably benign tumor composed of adipose tissue and hematopoietic elements. Due to the variable proportion of fat and hematopoietic elements, it is sometimes challenging to differentiate AML from adrenocortical carcinoma (ACC). MicroRNAs have been identified as promising biomarkers in many tumors, including adrenocortical neoplasms, but the microRNA expression of adrenal myelolipoma has not been investigated, yet. Aims: To perform a large scale microRNA expression profiling in adrenal myelolipoma, benign and malignant adrenocortical tumors to identify potential microRNA biomarkers. Methods: Next-generation sequencing (NGS) on 30 formalin-fixed paraffin-embedded archived tissue samples (discovery cohort: 10 adrenocortical adenoma (ACA), 10 ACC and 10 myelolipoma) was performed by Illumina MiSeq. Significantly differentially expressed microRNAs were validated by real-time RT-qPCR in an independent validation cohort comprised of 10 ACA, 10 myelolipoma and 9 ACC samples. Results:  We have found relative overexpression of miR- 451a, miR-486-5p, miR-363-3p and miR-150-5p in myelolipoma compared to the other two tumor groups by NGS. For ACC, we have found  up-regulation of miR-184, miR-483-5p, miR-431-5p and miR-183-5p compared to myelolipoma and ACA. Validation by RT-qPCR, confirmed significant overexpression of miR-451a, miR-486-5p and miR-150-5p in myelolipomas relative to ACA and ACC, whereas  significant overexpression of miR-184 and miR-183-5p was confirmed in ACC relative to the other 2 groups. The overexpression of miR-483-5p has not turned out to be significant in ACC relative to myelolipomas in the validation cohort. Conclusions: Overexpressed miR-451a, miR-486-5p and miR-150-5p might be potential tissue markers of adrenal myelolipoma. The lack of significance in the expression of miR-483-5p between ACC and myelolipoma is remarkable, as miR-483-5p has been considered to be the best marker of adrenal malignancy to date. Altogether 30 samples were investigated by high-throughput microRNA expression profiling