What is "cancer" in one article?
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What is cancer
Cancer is the name of a group of related diseases. In all types of cancer, certain cells in the body begin to divide without stopping and spread into the surrounding tissues.
Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, the body's cells grow and divide to form new cells as the body needs them. When cells become old or damaged, they die and new cells will replace them.
However, when cancer develops, this orderly process breaks down. As the cells become more abnormal, old or damaged cells should survive death while new cells are formed when they are not needed. These extra cells can divide without stopping and may form a growth called a tumor.
Many cancers form solid tumors, or solid tumors. Cancers of the blood, such as leukemia, do not usually form solid tumors.
Cancerous tumors are malignant, which means they can spread to or invade nearby tissues. In addition, as these tumors grow, some cancer cells can rupture and spread through the blood or lymphatic system to distant parts of the body and form new tumors far from the original tumor.
Unlike malignant tumors, benign tumors do not spread to or invade nearby tissues. However, benign tumors can sometimes be very large. After removal, they usually do not grow back, while malignant tumors sometimes do. Unlike most benign tumors in other parts of the body, benign brain tumors can be life-threatening.
The difference between cancer and normal cells
Cancer cells are different from normal cells in many ways; they can grow uncontrollably and are aggressive. One important difference is that cancer cells are less specialized than normal cells. That is, normal cells mature into distinct cell types with specific functions, whereas cancer cells do not. This is one reason why, unlike normal cells, cancer cells continue to divide without stopping.
In addition, cancer cells are able to ignore signals that normally tell the cell to stop dividing or to begin a process known as programmed cell death or apoptosis, and the body uses these signals to remove unwanted cells.
Cancer cells may be able to affect the normal cells, molecules and blood vessels that surround and feed the tumor, an area called the microenvironment. For example, cancer cells can induce nearby normal cells to form blood vessels that provide the tumor with the oxygen and nutrients it needs to grow. These blood vessels also remove waste products from the tumor.
Cancer cells are also usually able to escape the immune system, a network of organs, tissues and specialized cells that protect the body from infections and other diseases. Although the immune system can usually remove damaged or abnormal cells from the body, some cancer cells can still "hide" in the immune system.
Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent uncontrolled immune responses, cancer cells can actually prevent the immune system from killing cancer cells. , , and
How Cancer Appears
How cancer appears
Cancer is caused by certain changes in genes (the basic physical units of inheritance). Genes are arranged in long strands of tightly packed DNA called chromosomes. Cancer is an inherited disease, which means that it is caused by changes in the genes that control the function of our cells, especially the way they grow and divide.
The genetic changes that cause cancer can be inherited from our parents. They can also be caused during a person's lifetime by errors caused by cell division or by damage to DNA caused by certain environmental exposures. Environmental exposures that cause cancer include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet light from the sun. (Our Cancer Causes and Prevention section provides more information.) Each person's cancer has a unique combination of genetic changes. As the cancer continues to progress, other changes occur. Even within the same tumor, different cells may have different genetic changes.
Often, cancer cells have more genetic changes, such as DNA mutations, than normal cells. Some of these changes may not be related to cancer. They may be the result of the cancer, not the cause.
The "drivers" of cancer
Genetic changes that cause cancer tend to affect three main types of genes - proto-oncogenes, oncogenes and DNA repair genes. These changes are sometimes referred to as "drivers" of cancer.
Proto-oncogenes are involved in the growth and division of normal cells. However, when these genes are altered in some way or are more active than normal, they can become oncogenes (or cancer genes), which allow cells to grow and survive when they should not.
Tumor suppressor genes are also involved in controlling cell growth and division. Cells with certain alterations in tumor suppressor genes may divide in an uncontrolled manner.
DNA repair genes are involved in repairing damaged DNA. cells with mutations in these genes tend to have other mutations in other genes. Together, these mutations may cause cells to become cancerous.
As scientists learn more about the molecular changes that cause cancer, they are finding that certain mutations commonly occur in many types of cancer. Thus, sometimes cancers are characterized by the types of genetic changes thought to cause them, not just by how they develop in the body and how the cancer cells look under a microscope.
Spread of cancer
During metastasis, cancer cells break away from the location where they first formed (primary cancer), spread through the blood or lymphatic system, and form new tumors elsewhere in the body (metastatic tumors). Metastatic tumors are the same type of cancer as the primary tumor.
Cancer that has spread to another part of the body from its initial start is called metastatic cancer. The process of spreading cancer cells to other parts of the body is called metastasis.
Metastatic cancer has the same name and type as the original or primary cancer. For example, breast cancer that spreads and forms metastatic tumors in the lungs is metastatic breast cancer, not lung cancer.
Under the microscope, metastatic cancer cells usually look identical to the original cancer cells. In addition, metastatic cancer cells and the original cancer cells usually share certain molecular characteristics, such as the presence of specific chromosomal changes.
Treatment may help prolong the lives of some patients with metastatic cancer. However, in general, the primary goal of treating metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by the cancer. Metastatic tumors can severely impair body functions, and most people who die from cancer will die from metastatic disease.
Types of cancer
There are more than one hundred types of cancer. The types of cancer are usually named according to the organ or tissue where the cancer forms. For example, lung cancer begins in the cells of the lungs and brain cancer begins in the cells of the brain. Cancers can also be described by the type of cells that form them, such as epithelial cells or squamous cells.
1. Carcinoma
Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are cells that cover the inner and outer surfaces of the body. There are many types of epithelial cells, which usually have a cylindrical shape when viewed under a microscope. Adenocarcinomas are cancers that form in epithelial cells that produce fluid or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissue. Most cancers of the breast, colon and prostate are adenocarcinomas. Basal cell carcinomas are cancers that begin in the lower or basal (foundation) layer of the epidermis, which is the outer layer of a person's skin.
Squamous cell carcinomas are cancers that form in the squamous cells, which are epithelial cells that lie beneath the outer surface of the skin. Squamous cells are also located in many other organs, including the stomach, intestines, lungs, bladder and kidneys. When viewed under a microscope, squamous cells look as flat as fish scales. Squamous cell carcinoma is sometimes called epidermoid carcinoma.
Migratory cell carcinoma is a type of cancer that forms in the epithelial tissue called the epithelium or urothelium. This tissue consists of many layers of epithelial cells that can grow larger and larger and are distributed in the inner layers of the bladder, ureter, part of the kidney (renal pelvis), and some other organs. Some cancers of the bladder, ureter and kidney are metastatic cell carcinomas.
2. Sarcoma
Soft tissue sarcomas form in the soft tissues of the body, including muscles, tendons, fat, blood vessels, lymphatic vessels, nerves, and tissues around joints. Sarcomas are cancers that form in the bones and soft tissues, including muscles, fat, blood vessels, lymphatic vessels and fibrous tissues (such as tendons and ligaments).
Osteosarcoma is the most common type of bone cancer. The most common types of soft tissue sarcomas are smooth muscle sarcoma, Kaposi's sarcoma, malignant fibrous histiocytoma, liposarcoma and augmentation skin sarcoma.
3. Leukemia
Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers do not form solid tumors. Instead, large numbers of abnormal white blood cells (leukemia cells and leukemia mother cells) accumulate in the blood and bone marrow, crowding out normal blood cells. Low levels of normal blood cells make it more difficult for the body to absorb oxygen into tissues, control bleeding or fight infection.
There are four common types of leukemia, grouped according to how quickly the disease progresses (acute or chronic) and the type of blood cells (lymphocytes or myeloid cells) in which the cancer begins.
4. Lymphoma
Lymphoma is a cancer that begins in lymphocytes (T or B cells). These are the white blood cells that fight disease and are part of the immune system. In lymphoma, abnormal lymphocytes accumulate in lymph nodes, lymphatic vessels, and other organs of the body.
There are two main types of lymphoma: Hodgkin's lymphoma - People with this disease have abnormal lymphocytes called Reed-Sternberg cells. These cells are usually formed from B cells. Non-Hodgkin's lymphoma - This is a large group of cancers that originate from lymphocytes. The cancer can grow quickly or slowly and can be formed by B cells or T cells.
5. Multiple myeloma
Multiple myeloma is a cancer that begins in plasma cells (another type of immune cell). Abnormal plasma cells called myeloma cells accumulate in the bone marrow and form tumors throughout the bones of the body. Multiple myeloma is also known as plasma cell myeloma and Kaller's disease.
6. Melanoma
Melanoma is a type of cancer that begins in cells that become melanocytes, specialized cells that form melanin (the pigment that gives skin its color). Most melanomas form in the skin, but melanomas can also form in other colored tissues, such as the eyes.
7. Brain and spinal cord tumors
There are different types of brain and spinal cord tumors. These tumors are named according to the type of cells from which they form and the location in the central nervous system where the tumor first forms. For example, astrocytic tumors begin in astrocytes called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancerous) or malignant (cancerous).
8. Other types of tumors
Germ cell tumors : Germ cell tumors are tumors that begin in the cells that produce sperm or eggs. These tumors can occur almost anywhere in the body and can be benign or malignant.
Neuroendocrine tumors: Neuroendocrine tumors are formed by cells that release hormones into the bloodstream in response to signals from the nervous system. These tumors, which may produce higher than normal levels of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.
9. Carcinoid tumors
Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most commonly in the rectum and small intestine). Carcinoid tumors may spread to the liver or other parts of the body and may secrete substances such as serotonin or prostaglandins, leading to carcinoid syndrome.