Diagnostic and Prognostic Value of MicroRNA in Breast Cancer Patients

Breast cancer ( BC) is the most commonly diagnosed cancer in women worldwide. The incidence and mortality rates for female breast cancer far exceeded those for other cancers . Although the incidence rate of breast cancer has risen, the mortality rates have steadily fallen due to early diagnosis and better treatments . Early detection of breast cancer often leads to better outcomes. According to Cancer Australia's National Cancer Control Indicators, the relative survival for females diagnosed with early-stage breast cancers at diagnosis was much higher than that for those with advanced breast diagnosis.

Despite the improvement in diagnosis and treatment,approximately 20% of BC patients will develop metastasis.This setting is considered an incurable disease that often occurs due to either resistance to therapy or diagnosis at advanced stages . In this scenario, although 44% of the patients are diagnosed at stage I (AJCC cancer staging) with 5-year survival rates of 100%, 5% of patients are diagnosed at stage IV with 5-year survival rates of approximately 26% .

The small percentage of women diagnosed at advanced stage of the disease gives evidence that mammography represents the best available screening option for breast cancer .

However, more accurate and meaningful early-diagnosis methods together with image techniques would improve BC survival rates.

MicroRNAs (MiRNAs) are short endogenous noncoding RNA molecules of 19-25 nt that have important gene regulatory roles at post-transcriptional level [8, 9]. They pair with messenger RNAs (mRNAs) of protein-coding genes and depending on complementarity, leading to mRNa translational repression or degradation . They regulate 30% of transcripts and contain 3% of the human genome .

In the past few years, miRNAs were established as relevant molecular components of cells in normal or malignant processes.. Particularly, miRNAs have been demonstrated to have an important role in cancer biology through post transcriptional editing of target messenger RNAs expression involved in tumor growth, invasion, metastasis or immune escape .

In addition, several tumor-associated miRNA profiles have been proposed and investigated as biomarkers for diagnosis, survival, response to treatment or tumor subclassification.

The development of early diagnostic tools is of most interest to the clinics since early diagnosis is associated with better prognosis.

In this context, miRNAs have been demonstrated to be good early diagnostic biomarkers in several types of cancer including BC, among others.

One of the main advantages of circulating miRNAs is their high stability in body fluids , which is the main reason for them to be used in cancer diagnosis or prognosis.

Moreover, the assessment of circulating miRNAs can be carried out with simple, lowcost and quick assays.

These characteristics highlight the value of miRNAs as non-invasive biomarkers. Indeed, several miRNAs have been found to be differentially expressed in blood, plasma or serum from healthy donors compared with BC patients, supporting their use as noninvasive, early-stage diagnosis biomarkers.

Growing evidences revealed that imaging techniques are associated with some limitations such as expensive. Hence, it seems that utilization of improvement imaging techniques and biochemistry biomarkers could overcome the limitations associated with imaging techniques. Beside utilization of imaging techniques, identification of new biomarkers in patients with breast cancer has provided an interesting landscape .

So studies have identified different circulating miRNAs as new biomarkers for BC detection; Moreover, they have not been assessed in conjunction with diagnostic imaging, which is used for quantifying the extent of the disease and provides information related to tumour aggressiveness representing an obligatory step for treatment planning. The use of diagnostic imaging to extract quantitative parameters related to the morphology, metabolism and functionality of tumours, as well as to correlate specific imaging parameters with molecular biomarkers, is an emerging research topic