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Background
Cancer is the second most common cause of death, being responsible for 8.2 million deaths worldwide in 2013 [1, 2]. Of particular interest is that in industrialised countries the incidence of cancer is much higher than that seen in less developed countries [2]. The incidence in these less developed countries is expected to rise due to the growth and ageing of their populations along with an increase in the prevalence of known risk factors [3]. In males, lung cancer is the leading cause of cancer worldwide deaths, while for women this is the case only in industrialised countries, while in less developed countries breast cancer is the leading cause of cancer deaths [1, 2]. Cancer has been characterised by the mutations of somatic genes that alter the function of the protein(s) they encode for [4]. Somatic alterations have been observed in most solid tumours such as those of the colon, breast, brain and pancreas. Nearly all (95%) of these altered mutations are single base substitutions, while the other 5% result from the insertion or deletion of one or a few base pairs [4]. Cancer is not a single disease with more than 100 different types known [5]. There is an extensive heterogeneity present between the same type of tumour in different individuals (intertumour heterogeneity) and among cancer cells within the same tumour (intratumour heterogeneity) [6]. Primary tumours are genetically heterogeneous and consist of multiple subpopulations of cancer cells which differ with respect to genotype(s) and phenotype(s) [7].
In the recent years, there has been a significant progress; in the diagnosis, treatment and prevention of some types of cancer [8]. Currently cancer treatments, involve surgery, chemotherapy, radiation, biological and hormonal therapy. However, the main problems with these current treatments are their high cost and adverse side effects [9]. Doxorubicin is a conventional chemotherapeutic agent that is widely used in the treatment of many tumours. However, it causes oxidative stress-mediated injury to the kidney [10], heart [11], and brain [12]. Metastatic breast cancer resistance to chemotherapeutic agents remain an obstacle for effective treatment. Chemotherapeutic agents such as taxanes and anthracyclines are not effective in controlling breast cancer as this tumour develops resistance to such drugs [13]. The overall median survival of patients with brain metastases from...