Breastcancer is the most frequently diagnosed cancer and the second leading cause of cancerdeaths among women. In 2017, an estimated number of 252,710 new breast cancer casesare expected to be diagnosed in women in the United States; accounting for 30% ofall new cancer diagnoses in women (Siegel et al.
, 2017). As of 2015, 570,000women have died from breast cancer; accounting for 15% of all cancer deathsamong women (DeSantis et al., 2016). Ingeneral, overall survival rates for all age groups have increased over timewith the 5- and 10- year survival rates for breast cancer cases being 90% and83% 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% forregional stage (cancers that have spread to surrounding tissue or neighbouringlymph nodes) but 26% for distant stage (cancers that have metastasized todistant organs or lymph nodes above the collarbone) disease (Siegel et al., 2017). However,survival rates show strong correlation to the cancer stage at diagnosis, withmetastasis accounting for 90% of cancer deaths (Gupta and Massague, 2006). Metastasisoccurs when cancer cells detach from the primary tumour and adapt to distant tissuesand organs to form a secondary tumour; forming the hallmark of malignanttumours (Camarillo et al,.
2012). Metastasis is achieved through successful completionof multiple sequential series of cell-biological events collectively called theinvasion-metastasis cascade where tumour cells exit their primary growth sites(local invasion, intravasation), translocate systemically (survival incirculation, arrest at a distant organ site, extravasation) before adapting tosurvive and thrive in the foreign microenvironments of distant tissues(micromestasis formation, metastatic colonization) (Valastyan and Weinberg,2011).