In this study, the serum levels of miR21 and miR10b were significantly upregulated in patients with BC with a median fold change (16.9 and 29.2, respectively) compared to healthy controls with a median fold change (0.6 and 1.3, respectively) (P = 0.001).
In agreement with these results, previous studies [16,17,18,19] have found that the serum level of miR21 was significantly upregulated in patients with BC compared to healthy controls (P = 0.0001).
ROC curve analysis was done to assess the validity of serum miR21 and miR10b as diagnostic markers for BC. In this study, miR10b and miR21 have demonstrated a strong discriminating ability between patients with BC and healthy controls. ROC curve analysis demonstrated an AUC of 0.965, sensitivity of 95.7%, and specificity of 85%, at a cutoff value of 1.7 for miR21 and an AUC of 0.991, sensitivity of 97%, and specificity of 100% at a cutoff value of 3.1 for miR10b. Therefore, miR21 and miR10b can be useful biomarkers for distinguishing between healthy controls and patients with BC. However, both markers could not discriminate between various stages of BC or between metastatic and nonmetastatic groups.
The focus of this work was a marker for the early detection of BC, as this would offer patients a significantly higher survival rate. When BC is detected in the early stages (stages I and IIA), the survival rate is 87%, whereas it drastically drops to 13% in stage IV with late detection. Mammography in the early stages in tumors < 2 cm has a sensitivity of 88% and a specificity of 93% , whereas core biopsy and FNAC have a sensitivity of 97% and specificity of 92%; however, both require expertise and are invasive procedures .
The latest guidelines  for screening patients with BC aimed to detect cancer in the early stages, so it is recommended to have annual mammography done. Furthermore, women at high risk of BC (positive family history and BRCA mutations) would benefit from mammography and annual screening with magnetic resonance imaging.
The median levels of serum miR21 and miR10b in patients with BC stages (I and IIA) (14.2 and 21.1, respectively) were statistically significantly higher compared to healthy controls (0.5 and 1.3, respectively; P < 0.001).
ROC analyses were plotted to assess the sensitivity, specificity, and diagnostic accuracy of these markers, which were found to be superior in the early detection of BC. miR21 at a cutoff value of 2.6 showed a sensitivity of 100%, specificity of 90%, and diagnostic accuracy of 93%. miR10b at a cutoff value of 3.1 showed a sensitivity of 91.7%, specificity of 95%, and diagnostic accuracy of 93%. Those findings highlighted their role as useful early diagnostic biomarkers for distinguishing early-stage patients with BC from healthy controls.
Positive HER2 expression was found to promote tumor aggression, invasion, and progression . The relationship between miR21 and HER2 was investigated in this work in several clinicopathologic aspects. There was a significant finding only regarding menopausal status. The serum level of miR21 was statistically significantly higher in premenopausal patients with BC than postmenopausal patients (P = 0.008). Similarly, the incidence of HER2-positive patients was higher in the premenopausal group compared to the postmenopausal group (14/25 versus 12/45; P = 0.02).
However, there was no statistically significant difference in the expression level of miR21 regarding HER2 status (P = 0.841). This finding was similar to a previous study [16, 20]. Therefore, miR21 might be independent of HER2 status.
Regarding PR status, the miR21 expression level was statistically significantly higher in PR-positive than PR-negative patients (P = 0.018). Also, the miR21 level was statistically significantly higher in double-positive hormone receptor patients (ER+/PR+) than other combined hormonal receptor patients (ER+/PR−, ER−/PR+, and ER−/PR−; P = 0.034). These results were similar to a study done by  that found miR21 level was statistically significantly higher in PR-positive than in PR-negative patients (P = 0.018) and statistically significantly higher in certain combined hormonal receptor status groups (ER+/PR+) than in the combined hormonal receptor (ER+/PR−, ER−/PR+, and ER−/PR−; P = 0.006).
The prognosis of patients with BC and response to endocrine therapies are highly influenced by ER and PR expression levels. Unfortunately, some patients become resistant to standard therapies. That is why it is important to add additional factors, such as miR21. This will not only be valuable for patient stratification but also in searching for new kinds of therapeutics, such as anti-miR therapy .
The results showed no statistically significant difference in the expression level of miR21 or miR10b regarding ER status (P = 0.066 and 0.758). Similarly, there was no statistically significant difference in the expression level of miR21 or miR10b regarding BC grade or pathology (duct and lobular; P = 0.305, 0.128, 0.207, and 0.660, respectively) and different clinical stages and BC subtypes (luminal A, luminal B, basal, and enriched; P = 0.435, 0.674, 0.29, and 0.761, respectively). No statistically significant difference in the expression level of miR21 or miR10b in patients with BC regarding lymph node metastasis (P = 0.725 and 0.618, respectively) or different metastatic sites (bone, brain, lungs, and liver; P = 0.583 and 0.194, respectively) was found.
The limitation of our study is although this is the recommended sample size however bigger sample size would be more informative if more patients in the early stage were included.