1.1 INTRODUCTION
Cancer is a group of diseases that affects the human body. It manifests through the proliferation of previously healthy cells into tumor cells by some causative factors. Different types of cancers numbering over 200 are now known and classified based on the type of cell that is initially affected. For instance, cancers arising from epithelial cells are called carcinoma, those from connective tissue are called sarcoma, and those from hematopoietic (blood-forming) are called lymphoma and leukemia while those from pluripotent cells and immature “precursor” cells/embryonic tissue are respectively known as germ cell tumor and blastoma. The transformation of healthy cells can give rise to tumor cells which eventually becomes cancer through a multistage process usually from a pre-cancerous lesion to a malignant tumor (WHO, 2018a). In the disease condition, old cells do not die, instead grows out of control, forming new abnormal cells. These abnormal cells often result in a tumor although some kinds of cancers do not form tumors, e.g., leukemia. The tumor can grow and obstruct the function of the nervous, digestive, and circulatory systems, with the possibility of releasing hormones that can alter the body functions. Tumors that do not spread and with limited growth are called benign tumors while those capable of spreading are called a malignant tumor. There are six hallmarks criterion for malignant tumor formation. They include cell growth and division, continuous growth and division even when given contrary signals, circumventing programmed cell death, uncontrolled number of cell divisions, promoting blood vessel construction, metastases formation and invasion of tissue (Hanahan and Weinberg, 2000). The potential signs and symptoms of cancer include unusual bleeding or discharge (blood in the urine, bleeding between periods, blood during cough and vomit), lump in the breast, coughing, chest pain and breathlessness, changes in bowel or bladder habits, indigestion or difficulty in swallowing, a sore that does not heal, obvious changes is warts or moles, and unexplained weight loss.
In the United States alone, cancer is notoriously the second leading cause of death after heart disease which has retained the number one spot for the past 15 years (CDC, 2017). One-half of men and one-third of women have a lifetime cancer risk. In 2015, about 90.5 million people worldwide had cancer which resulted in 8.8 million deaths (15.7% of deaths) (GBD, 2016). Yearly, about 14.1 million new cases occur excluding skin cancer. According to WHO (2018a), the most prevalent type of cancers is lung cancer which caused 1.69 million deaths, liver cancer which caused 788,000 deaths, the colorectal cancer which led to 774,000 deaths, stomach cancer which caused 754,000 deaths and the breast cancer which caused 571,000 deaths. Approximately, 70% of these deaths occur in the low- and middle-income countries. This may partly be because of the lack of early-stage screening facilities or poor diagnostic conditions. In 2017, it was found that only 26% of low-income countries have pathology services available in the public sector compared to more than 90% for high-income countries (WHO, 2018a). Globally, about one in six deaths are caused by cancer. A major fraction, 90–95% of cases of cancer, are as a result of genetic mutations which is influenced by environmental factors (not genetically inherited, e.g., lifestyle, behavioral, and economic factors), while the remaining 5–10% cases of cancer are due to inherited genetics (Anand et al., 2008). From records, it was found that one-third of deaths from cancer are linked to five leading behavioral and dietary risks. These are high body mass index, lack of physical activity or exercise, low consumption of fruits and vegetables, tobacco, and alcohol use. These factors culminate between a person’s genetic factors and three categories of external agents, including: physical carcinogens, such as radiations (ultraviolet, ionizing radiation, etc.); chemical carcinogens, e.g., asbestos, benzidine, aristolochic acids, mists from strong inorganic acids, e.g., sulfuric acid, formaldehyde, aflatoxin (a food contaminant), tobacco smoke components, arsenic; biological carcinogens, e.g., infections of certain viruses (e.g., human papillomavirus (HPV), Hepatitis B and C viruses, Kaposi sarcoma-associated herpesvirus (KSHV) and human T-cell leukemia/lymphoma virus type-1 (HTLV-1), bacteria (e.g., Helicobacter pylori), or parasites (e.g., Opisthorchis viverrini, Schistosoma haematobium). Up to 25% of cancer cases result from hepatitis and HPV infections in low- and middle-income countries (Plummer et al., 2016).
According to the American Cancer Society (2018), the increasing cases of deaths from cancer can be prevented by systematic approach by improved lifestyle through proper dieting and physical activity, reduction of tobacco use, good dieting, physical activities, and the use of tobacco and application of established screening tests. It can reduce death from cancer. In 2010, the total annual economic cost of cancer was estimated to be US$ 1.16 trillion (Stewart et al., 2014). However, there appear some prospects from the advent of new techniques for cancer research in molecular biology and biochemistry together with the declaration of “War on Cancer.”
1.1.1 EARLY DETECTION OF CANCER
The destructive effects of cancer can be reduced if cases are detected and treated early. The early detection of cancer may lead to decreased morbidity with improved survival, and in some situations treatment may require only surgery if identified early enough (Schiffman et al., 2015). The two basic components of early detection are early diagnosis and screening. In early detection, education plays a vital role in creating awareness for possible warning signs of cancer, among physicians, nurse...
