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Breast
cancer is the most frequently diagnosed cancer and the second leading cause of cancer
deaths among women. In 2017, an estimated number of 252,710 new breast cancer cases
are expected to be diagnosed in women in the United States; accounting for 30% of
all new cancer diagnoses in women (Siegel et al., 2017). As of 2015, 570,000
women have died from breast cancer; accounting for 15% of all cancer deaths
among women (DeSantis et al., 2016).

 

In
general, overall survival rates for all age groups have increased over time
with the 5- and 10- year survival rates for breast cancer cases being 90% and
83% respectively. The 5-year survival rate between 2006 to 2012 ranges from 99%
for localized stage (cancers that are confined to the breast) to 85% for
regional stage (cancers that have spread to surrounding tissue or neighbouring
lymph nodes) but 26% for distant stage (cancers that have metastasized to
distant organs or lymph nodes above the collarbone) disease (Siegel et al., 2017).

 

However,
survival rates show strong correlation to the cancer stage at diagnosis, with
metastasis accounting for 90% of cancer deaths (Gupta and Massague, 2006).

 

Metastasis
occurs when cancer cells detach from the primary tumour and adapt to distant tissues
and organs to form a secondary tumour; forming the hallmark of malignant
tumours (Camarillo et al,. 2012). Metastasis is achieved through successful completion
of multiple sequential series of cell-biological events collectively called the
invasion-metastasis cascade where tumour cells exit their primary growth sites
(local invasion, intravasation), translocate systemically (survival in
circulation, arrest at a distant organ site, extravasation) before adapting to
survive and thrive in the foreign microenvironments of distant tissues
(micromestasis formation, metastatic colonization) (Valastyan and Weinberg,
2011). 

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