not produce these substances and can therefore spread to other body locations via the bloodstream or lymphatic system.
Ability to metastasize (spread): Normal cells remain in the same area of the body where they serve a particular function, e.g. kidney cells remain in the kidneys. Due to their lack of cohesion, cancer cells are able to move through the bloodstream and lymphatic system to other locations of the body. In these new locations, they have the ability to metastasize, forming tumors distant from the original tumor.
Rate of growth: Normal cells reproduce themselves in a controlled, orderly process, but cease reproducing when enough cells are present. Cancer cells reproduce at abnormal rates, often rapidly and with no stopping mechanism.
Maturation: Normal cells mature with age, whereas cancer cells remain immature and continue to reproduce unchecked before they are fully mature.
Evade the immune system: The human body's immune system is a network of organs, tissues, and specialized cells that keeps the body protected from infections and other harmful conditions. When normal cells become damaged, the immune system identifies and removes them. Cancer cells are able to evade removal by the immune system, resulting in the formation of tumors.
Energy source: In the presence of oxygen, normal cells produce most of their energy supply. Cancer cells have changed, however, and are able to produce energy without oxygen. This capacity to generate energy for growth and survival without oxygen (a condition found inside a tumor) enables cancer cells to thrive where normal cells die.
1.4 Types of Cancer
There are more than 200 types of cancer, with researchers classifying them based on the location of origin [4]. Four major types of cancer are:
1.4.1 Carcinomas
This is the most common type of cancer. A carcinoma starts in the skin or in the tissue that covers the surface of internal organs and glands. Carcinomas normally form solid tumors. Examples include prostate cancer, breast cancer, lung cancer, and colorectal cancer.
1.4.2 Sarcomas
A sarcoma occurs in the tissues that support and connect the body, including fat, muscles, nerves, tendons, joints, blood vessels, lymph vessels, cartilage, or bone.
1.4.3 Leukemias
Leukemia is blood cancer that occurs when healthy blood cells change and develop uncontrollably. The four main types of leukemia include acute lymphocytic leukemia, chronic lymphocytic leukemia, acute myeloid leukemia, and chronic myeloid leukemia.
1.4.4 Lymphomas
Lymphomas start in the lymphatic system. The lymphatic system is a network of vessels and glands that protects the human body from infection. There are two main kinds of lymphomas: Hodgkin lymphoma and non‐Hodgkin lymphoma.
1.5 The Role of Genes and Chromosomes
In the nucleus of each cell, there are the thread‐like structures that package deoxyribonucleic acid (DNA) called chromosomes. Chromosomes are found in all living cells and consist of a single molecule of DNA bound to various proteins (Figure 1.3). They carry the genes, which are the basic units determining inherited traits. Genes control cell function, particularly how cells grow and divide, and when they need to stop this growth [5–14].
Figure 1.3 Cell structure showing DNA in the nucleus. The DNA molecule is a double helix. A gene is a length of DNA that codes for the manufacture of a specific protein.
In the human body, there are 46 chromosomes, arranged in 2 sets of 23. We inherit one set from our mother and one from our father. Chromosomes contain all the information for the physical characteristics that make up an individual. One chromosome in each set determines whether a person is female or male. The other 22 chromosome pairs decide other physical characteristics in the human body. These chromosome pairs are also called autosomes.
Genes regulate protein production. Each protein functions on its own and also carries messages for the cell. Each gene follows specific instructions, encoded in their genetic material, for producing proteins; each protein performs specific functions for the cell (Figure 1.4).
Figure 1.4 Information from DNA is used to make proteins from genes.
Cancers start when one or more genes mutate. Mutations, however, are a normal occurrence. Their results may be beneficial, harmful, or neutral, depending on the location within the gene where the change has taken place. Most of the time the body corrects the mutations and nothing unusual happens.
A single mutation will generally not produce cancer. Typically, cancer develops from multiple mutations over a lifetime, which is why cancer occurs more frequently in older people. Mutations have had more opportunities to occur the longer a person lives. Mutation of genetic material changes the instructions for protein formation, resulting in the production of an abnormal protein or sometimes prevention of a certain protein being formed. An abnormal protein cannot carry out its specific function correctly, possibly leading to uncontrolled cell multiplication and the start of cancer (Figure 1.5).
Figure 1.5 Cancer cells start as normal cells, which acquire mutations over time that change them to cancer cells.
1.6 Genetic Mutations
There are two basic types of genetic mutations:
1.6.1 Acquired Mutations
Mutations of this type are the most common cause of cancer, and when this occurs, it is called sporadic cancer. These mutations, initially affecting only a few cells in the body, damage the genes in these cells. Since these mutations are acquired, they do not pass from parents to children. Major factors contributing to acquired mutations include:
Tobacco
Ultraviolet (UV) radiation
Viruses
Age
1.6.2
