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Breast cancer is known to be one of the most common malignant and life
threatening cancers in woman worldwide. It can affect both woman and men,
however woman are around 100 times more likely to develop the disease. It is
estimated that there are 1,384,155 estimated new cases of breast cancer
worldwide with a near 459,000 related deaths (Tao, et al.2014).  Statistics from
GLOBOCAN 2012, show that around 1.7 million women were diagnosed with breast
cancer and 522,000 related deaths (Tao, et
al.2014). Although there are various factors such as, life style and environmental
factors that affect the risk of breast cancer, the genetic factors are particularly
important when it comes to breast cancer development.

There are different types of breast cancers, Ductal carcinoma in
situ (DCIS) and Lobular carcinoma in situ (LCIS) being
the most common. DCIS is the most prevalent type of
non-invasive breast cancer, whereby cancers cells remain in situ in the breast ducts
due to their inability to spread into the normal tissue (Malhotra
et al., 2010). LCIS are cells that look like cancer cells; they grow in the
lobules of the breast and do not spread beyond (Malhotra et al., 2010).

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Whilst the exact causes of breast cancer are still yet to be known,
most breast cancers cells are sporadic and are mainly due to genetic and
environmental factors (ref).
 It is estimated that around 5 to 10% of
all breast cancers are hereditary, therefore it is determined by mutational
changes in a specific gene (Ratanaphan, 2012). The two genes, BRCA1 and BRCA2 are
mainly affected by the mutation, as they are the most common (Alhuqail et al,
2018). Hereditary breast and ovarian cancer syndrome (HBOC) is known to cause
50% of all hereditary breast cancers.  BRCA1
and BRCA2 are both involved in double stranded DNA break (DSBs) repair and are
the common genes in autosomal dominant and high penetrance form of HBOC. They work
by helping to maintain the cell’s genetic information and stopping cells from dividing
in an uncontrolled way. BRCA increases the lifetime risk of developing breast
cancer due to its pathogenic mutations (Alhuqail et al, 2018). They have a function to
produce tumour suppressor genes (TSG), meaning they act as a negative regulator
of tumour growth (Mehrgou and Akouchekian, 2016). Through mechanisms
such as, homologous recombination and DSBs, BRCA1 plays a crucial role in in
the repair of cellular DNA damage (Ratanaphan, 2012).  The BRCA1 gene was first mapped on chromosome 17q in 1990, contains
1863 amino acids and has two non-coding exons (Miki, et al. 1994). The BRCA1
gene has many functions in cellular processes including, DNA repair, cell cycle
regulation, protein ubiquitination and more (Ratanaphan, 2012)
 Evidence suggests that so far, BRCA1
contains around 300 disease-causing mutations in the gene and there are more
reported incidences of BRCA1 carriers than BRCA 2 carriers (Mehrgou and Akouchekian.2016).
The BRCA1 protein is mainly always present in normal breast tissue, whereas in
some breast tumours the protein is either reduced, altered or absent. Patients
who have the BRCA1 predisposing alleles, the wild-type copy of BRCA1 is
invariably lost when chromosome loss occurs in breast and ovarian tumours,
while the presumptive mutant allele remains (Peshkin, Alabek and Isaacs, 2011). The
dominantly expressed gene variations resulting from single-nucleotide
polymorphisms (SNP) are due to the heterogeneity of breast cancer and the
variations that manifest as a consequence of tumour progression (Hirotsu et al. 2014). For BRCA1 mutation
carriers there is a lifetime breast cancer risk ranging from 65% to 81% (Shah, Rosso and Nathanson, 2014). They have
a higher mitotic rate and more lymphatic penetrance in comparison with sporadic
breast cancer.

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