Fundamentals of Cancer Detection, Treatment, and Prevention - Surya K. De

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they should die, and new cells form when they are not required. These extra cells may divide without stopping, forming growths called tumors or cancers. The cancer cells continue to grow and make new cells, resulting in issues in the location where they began (Figure 1.1).

      Not all tumors are cancers. There are two types of tumors: malignant and benign. Malignant tumors are dangerous, as they can spread into, or invade, nearby tissues. When these tumors grow, a few cancer cells can break away and spread to other parts of the body through the blood or lymphatic system, resulting in the development of new tumors distant from the original tumor.

      Benign tumors are not as dangerous. They do not spread into, or invade, nearby tissues or organs. Benign tumors can be large or small. When removed, they usually do not come back, whereas malignant tumors do. Nonetheless, if a benign tumor is located in a sensitive place like the brain, it can still cause some problems.

      Cancer is a major public health problem worldwide and the second leading cause of death after heart disease. Cancer has a huge impact on society in the United States and across the world. Statistical data documents the tremendous numbers of people diagnosed with cancer each year, along with mortality rates. These numbers are further broken down to show the incidence and effects of cancer within various groups defined by age, sex, ethnicity, geographic location, diet, lifestyle, and other factors.

Schematic illustration of the human body contains internal organs and systems, any of which can be the origin of cancer.

      According to the World Health Organization:

       Cancer is the second leading cause of death globally, and is responsible for an estimated 10 million deaths in 2020, and an estimated 19.3 million new cancer cases.

       Globally, about 1 in 6 deaths is due to cancer.

       Approximately, 70% of deaths from cancer occur in low‐ and middle‐income countries.

Schematic illustration of cancer cells are less organized than normal cells and grow in an uncontrolled fashion.

      Growth: Normal cells stop reproducing when enough are present. For instance, if cells are required to repair a cut in the skin, new cells are no longer produced when there are enough cells present to fill the gap. Cancer cells, however, do not stop growing and reproducing, and their continuous growth results in the formation of a tumor.

      Communication: Cancer cells don't interact with other cells in the same way as normal cells. Normal cells respond to signals sent from other nearby cells to stop growing. Cancer cells do not respond to these signals.

      Cell repairandcell death: Regular cells are repaired or die (in a process called apoptosis) when they are damaged or get old. Cancer cells either are not repaired or do not undergo apoptosis. The p53 gene regulates cell repair and apoptosis. When this gene is mutated or inactivated, a tumor begins.

      Stickiness: Normal cells produce substances that keep them cohesive within a group, as opposed to cancer cells, which do 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.

      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.

      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.

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