Page 5 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

2 CHAPTER 1 Introduction

preventable cancers. For instance, during 2012–16, compared to the richest cities, the
death rate in the poorest cities was twice as high for cervical cancer and 40% higher
for lung and liver malignancies [4].
Many predisposing factors have been identified. The incidence of cancer is found
to be significantly associated with the age of 10–60 years. In addition, the male gen-
der is at higher risk of developing cancer than women [2]. Race is another important
factor for cancer progression. Highest incidence has been reported before 40 years
of age, among non-Hispanic whites and, after 40 years of age, amongst African-
Americans/blacks [5]. Cancer can be a dangerous health problem, particularly when
the tumor has metastasized to other organs. Four cancers: lung, bronchial, breast and
colorectal in women and lung, bronchial, prostate and colorectal in men account for
approximately 50% of cancer-related deaths.
Cancer immunology has long been studied. However, the molecular and cellu-
lar basis of tumor immunity is not fully understood. Advances in understanding the
basics of the immune system and advances in the treatment of infectious diseases
have had a major effect on the development of immunotherapy. The role of T cell
responses in tissue allograft rejection has been known since the 1950s. Since then, it
has been recognized that tumors occur in association with T-cell dysfunction, indi-
cating the importance of the immune system in the growth and development of can-
cer [6].
The identification of tumor-associated antigens (TAA), understanding of effector
T cell responses, and the role of regulatory and suppressor T cells have determined
the use of the immune system to treat cancer. Tumors refer to an enormous spectrum
of diseases that originate from uncontrolled cellular growth. Tumor is divided into
benign tumors and malignant tumors [7].
Cancers are further classified by their cell type and tissue of origin.

1.2 Cancer stem cell

Cancer stem cells (CSCs) have been described as the origin of several types of human
cancer. However, other reports have indicated that CSCs are derived from stem cells,
tissue commitment progenitor cells, or tissue cells [8–14].
Stem cells are recognized by two main properties: self-renewal and differentiation.
In CSCs, there is an unbalance between self-renewal and differentiation [15]. The
main step of alteration of natural stem cell to CSC is self-renewal step. Imbalance
between stimulating and inhibitory signaling in self-renewal and proliferation among
stem cells leads to malignancy [15].
CSCs are a small population of cancer cells. Only a small part of tumor with
CSCs phenotype, stemness, have self-renewal character can produce tumor and treat-
ment of tumor cannot destroy CSCs, but can kill other tumor cells [16,17].
The uncontrolled cell division can originate from several factors, such as viral
infections, chemical agents and mutations that lead to evasion of cells from the
checkpoints which control cell division [6]. It has been reported that some tumors