**5. Breast cancer**

Cancer is a mutation of healthy cells whose DNA was not repaired back to a homogenous status. This mutation is expressed through biomarkers and molecular subtypes that drive the severity and prognosis of said cancers [29]. The BRCA gene has gotten skewed in its role in breast cancer. Its primary role is to repair damaged DNA and is considered to be a tumor suppressor, but with a mutated form of this gene, it can cause breast cancer and this is what this gene is now known for, not its original function [30]. The BRCA1 & 2 gene mutation is one culprit of a familial genetic mutation identified through whole gene sequencing [31]. Patients can be evaluated for the BRCA1 & 2 mutation and know whether they carry this mutated form of the gene and take precautions to proactively screen more frequently and/ or make informed decisions about their plan of care, options, and further testing for tumor markers. The individualized plan of care and having the knowledge that the risk is greater for breast cancer may assist in a more active role between the patient and their provider to ensure early detection remains the focus [29]. Why is this so important? Women with this mutation have a much higher risk of developing breast cancer compared to the general population without this genetic mutation (see **Table 3**). The Online Mendelain Inheritance in Man (OMIM) provides guidance on the BRCA1 & 2 gene phenotype relationship in relation to the chromosomal location, inheritance, mapping, and gene/locus (see **Table 4**). Also, women with a history of epithelial ovarian cancer should consider being tested for the BRCA gene mutation and any other cancer genes that align with ovarian cancer risk [30].

Over 80% of BRCA1 mutations lose its ability to differentiate breast stem cells and as a result it cannot express three specific receptors: human epidermal growth factor, estrogen, and progesterone. BRCA2 mutations have a higher rate of ovarian cancer compared to BRCA1 mutations. Studies have found that to reduce the risk of breast and/or ovarian cancer for those with either BRCA1 or 2 mutation is to proactively have an oophorectomy [33]. This could be due to the decline in hormone fluctuation, especially hormone receptor sensitive breast cancers.

## **5.1 Diagnostic testing, prognosis, and susceptibility**

There are advanced diagnostic testing options rooted in next-generation sequencing technology that is available when testing for specific breast cancer mutations. Clinicians can order these tests once a diagnosis of breast cancer is determined. These include the following: next-generation sequencing (NGS), sequenced analytic data pipelines derived from NGS, anchored multiplex polymerase chain reaction (AMP) also derived from NGS. Other tests that determine the aggressive nature of the cancer, its recurrence risk, and what adjuvant therapies are needed based on genetic analysis:


**Table 3.**

*Percentage of breast cancer patient comparisons [30].*

#### *Breast Health and Preventive Screening DOI: http://dx.doi.org/10.5772/intechopen.112597*


*4 = multiple gene involvement.*
