Micro RNA-21 expression levels in invasive breast carcinoma with a non-invasive component

Invasive ductal carcinomas with a non-invasive component (IDC-DCIS) are classified as a group of invasive breast carcinomas, together with pure invasive ductal carcinomas of the breast (IDC). MicroRNA-21 (miR-21) has been characterized as a factor of breast cancer invasiveness, however the difference in miR-21 expression levels between IDC-DCIS and pure IDC tumors and the correlations with standard diagnostic and prognostic parameters inside the IDC-DCIS group are unknown. Our aim was to determine if miR-21 had the ability to distinguish these two invasive breast cancer groups. Levels of miR-21 expression were measured by a stem-loop quantitative Real-Time PCR (RT-qPCR) method. Expression levels of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (Her-2) and proliferative index Ki-67 were evaluated by immunohistochemistry. IDC-DCIS tumors had significantly lower levels of miR-21 expression in grade 2 (P=0.003, Mann-Whitney U test), ER positive (P=0.025, Mann-Whitney U test) and PR positive tumors (P=0.024, Mann-Whitney U test) than pure IDCs. miR-21 levels showed a different pattern of expression in IDC-DCIS compared to IDC tumors, which is based on the difference in miR-21 expression between Her-2 negative and Her-2 positive IDC-DCIS tumors (P=0.030, Mann-Whitney U test) and high negative correlation of miR-21 levels with PR levels (ρ=-0.886, P=0.006, Spearman correlation). According to our results, IDC-DCIS breast carcinomas act in a different manner in pure IDC tumors with regard to the relations between miR-21 expression levels and the standard diagnostic and prognostic parameters, such as Her-2 status, ER and PR status and protein levels