Cancer is a term used to describe a group of diseases characterised by abnormal cell growth that has the potential to invade or spread to other parts of the body. Benign tumours, on the other hand, do not spread.
WHAT DO YOU MEAN BY CANCER?
Cancer is a disease in which certain cells in the body grow out of control and spread to other parts of the body.
Cancer can begin almost anywhere in the trillions of cells that make up the human body. Human cells normally grow and multiply (through a process known as cell division) to form new cells as needed by the body. Cells die when they become old or damaged, and new cells replace them.
This orderly process can sometimes break down, resulting in abnormal or damaged cells growing and multiplying when they shouldn't. Tumors, which are lumps of tissue, can form from these cells. Tumors may or may not be cancerous (benign).
Cancerous tumours can invade nearby tissues and spread to other parts of the body, resulting in the formation of new tumours (a process called metastasis). Malignant tumours are another name for cancerous tumours. Many cancers, including leukemias, form solid tumours, but cancers of the blood do not.
Benign tumours do not invade or spread into nearby tissues. Benign tumours rarely reappear after being removed, whereas cancerous tumours do. However, benign tumours can grow to be quite large. Some, such as benign brain tumours, can cause serious symptoms or even be fatal.
DIFFERENCES BETWEEN CANCER CELLS AND NORMAL CELLS
Cancer cells are distinct from normal cells in a number of ways. Consider the following example:
• Cancer cells proliferate in the absence of growth signals. Normal cells can only grow in response to such signals.
• Cancer cells disregard signals that tell them to stop dividing or die (a process known as programmed cell death, or apoptosis).
• They spread to other parts of the body after invading nearby areas. When normal cells come into contact with other cells, they stop growing, and most normal cells do not move around the body.
• They instruct blood vessels to expand in the direction of tumours. These blood vessels provide oxygen and nutrients to tumours while also removing waste products.
• Cancer cells evade the immune system's detection. Damaged or abnormal cells are normally eliminated by the immune system.
• They persuade the immune system to assist cancer cells in surviving and growing. Some cancer cells, for example, persuade immune cells to protect the tumour rather than attack it.
• Cancer cells' chromosomes undergo a variety of changes, including duplications and deletions of chromosome parts. Some cancer cells have twice as many chromosomes as normal cells.
• Cancer cells are different from normal cells in that they require different types of nutrients. Furthermore, unlike most normal cells, some cancer cells generate energy from nutrients in a unique way. This allows cancer cells to multiply at a faster rate.
Cancer cells often rely on abnormal behaviours so heavily that they can't survive without them. This has led to the development of therapies that target the abnormal characteristics of cancer cells. Some cancer treatments, for example, stop blood vessels from growing toward tumours, effectively starving the tumour of nutrients.
Changes (mutations) in the DNA of cells are the cause of cancer. Each gene in a cell contains a set of instructions that tell the cell what functions to perform as well as how to grow and divide. Errors in the instructions can cause a cell to stop functioning normally and even cause it to become cancerous.
WHAT DO GENE MUTATIONS DO?
A healthy cell can be told by a gene mutation to:
• Allow for rapid expansion. A gene mutation can cause a cell to divide and grow more quickly. This produces a large number of new cells with the same mutation.
• Fail to halt uncontrolled cell proliferation. Normal cells know when to stop growing so that the number of each type of cell is just right. Tumor suppressor genes, which tell cancer cells when to stop growing, are lost in cancer cells. Cancer cells can continue to grow and accumulate due to a mutation in a tumour suppressor gene.
• When repairing DNA errors, make mistakes. DNA repair genes look for and correct errors in a cell's DNA. Other errors may not be corrected as a result of a mutation in a DNA repair gene, leading to cancerous cells.
These are the most common types of cancer mutations. However, many other gene mutations can play a role in the development of cancer.
WHAT CAUSES GENE MUTATIONS?
Gene mutations can occur for a variety of reasons, including:
• Gene mutations you inherit from your parents- You may inherit a genetic mutation from your parents. Only a small percentage of cancers are caused by this mutation.
• After-birth gene mutations—Most gene mutations happen after you're born and aren't inherited. Smoking, radiation, viruses, cancer-causing chemicals (carcinogens), obesity, hormones, chronic inflammation, and a lack of exercise are just some of the factors that can cause gene mutations.
During normal cell growth, gene mutations are common. Cells, on the other hand, have a mechanism that recognises when a mistake is made and corrects it. Occasionally, a blunder is overlooked. This has the potential to turn a cell cancerous.
HOW DO GENE MUTATIONS INTERACT WITH EACH OTHER?
Cancer is caused by a combination of gene mutations that you are born with and those that you acquire throughout your life.
For example, just because you've inherited a cancer-predisposing genetic mutation doesn't mean you'll get cancer. Instead, one or more other gene mutations may be required to cause cancer. When exposed to a cancer-causing substance, your inherited gene mutation may make you more likely to develop cancer than other people.
It's unclear how many mutations are required for cancer to develop. This is likely to differ depending on the type of cancer.
TYPES OF GENES THAT CAUSE CANCER
Proto-oncogenes, tumour suppressor genes, and DNA repair genes are all affected by the genetic changes that contribute to cancer. These changes are sometimes referred to as cancer's "drivers."
Proto-oncogenes play a role in normal cell division and growth. These genes can become cancer-causing genes (or oncogenes) if they are altered in specific ways or are more active than normal, allowing cells to grow and survive when they shouldn't.
Tumor suppressor genes are also involved in cell division and growth control. Certain mutations in tumour suppressor genes can cause cells to divide uncontrollably.
DNA repair genes are responsible for repairing damaged DNA. Cells with mutations in these genes are more likely to develop mutations in other genes and chromosome changes, such as chromosome duplications and deletions. These mutations may cause the cells to become cancerous if they occur together.
Scientists have discovered that certain mutations are common in many types of cancer as they learn more about the molecular changes that lead to cancer. Many cancer treatments are now available that target cancer-causing gene mutations. Anyone with a cancer that has the targeted mutation, regardless of where the cancer started growing, can use a few of these treatments.
WHEN CANCER SPREADS
Metastatic cancer is cancer that has spread from its original location in the body to another part of the body. Metastasis is the process by which cancer cells spread to other parts of the body.
Metastatic cancer has the same name as primary cancer and uses the same type of cancer cells. Breast cancer that has spread to the lungs, for example, is called metastatic breast cancer rather than lung cancer.
Metastatic cancer cells, when viewed under a microscope, resemble cells from the original cancer. Furthermore, metastatic cancer cells and cancer cells from the original tumour often share molecular characteristics, such as the presence of specific chromosome changes.
Treatment may help people with metastatic cancer live longer in some cases. In other cases, the primary goal of metastatic cancer treatment is to slow the cancer's progression or alleviate the symptoms it causes. Metastatic tumours can have a significant impact on how the body functions, and metastatic disease is the leading cause of death in cancer patients.
TISSUE CHANGES THAT ARE NOT CANCER
Not all changes in the tissues of the body are cancerous. However, if not treated, some tissue changes can progress to cancer. Here are some examples of tissue changes that aren't cancer but are monitored because they could turn into cancer in the future:
•Hyperplasia occurs when cells in a tissue multiply faster than normal, resulting in an overabundance of cells. Under a microscope, however, the cells and the way the tissue is organised appear to be normal. Chronic irritation is one of the factors or conditions that can cause hyperplasia.
•In comparison to hyperplasia, dysplasia is a more advanced condition. There is also a buildup of extra cells in dysplasia. However, the cells appear abnormal, and the tissue's organisation has changed. In general, the more abnormal the cells and tissue appear, the more likely cancer will develop. Some dysplasias require monitoring or treatment, while others do not. A dysplastic nevus (abnormal mole) that forms on the skin is an example of dysplasia. Although most dysplastic nevi do not develop into melanoma, some do.
•Carcinoma in situ is a more advanced form of cancer. Although it is sometimes referred to as stage 0 cancer, the abnormal cells do not invade nearby tissue in the same way that cancer cells do. However, because some carcinomas in situ have the potential to develop into cancer, they are usually treated.
TYPES OF CANCER
There are over 100 different types of cancer. Cancers are usually named after the organs or tissues in which they develop. Lung cancer, for example, begins in the lungs, while brain cancer begins in the brain. Cancers can also be classified based on the type of cell that caused them, such as epithelial or squamous cells.
You can use our A to Z List of Cancers or search the NCI website for information on specific types of cancer based on their location in the body. We also have information on cancers that affect children and cancers that affect adolescents and young adults.
Cancers that start in specific types of cells fall into the following categories:
The most common type of cancer is carcinoma. Epithelial cells, which cover the inside and outside surfaces of the body, are responsible for their formation. Many different types of epithelial cells exist, and when viewed under a microscope, they often have a column-like shape.
Carcinomas that start in different types of epithelial cells have different names:
Adenocarcinoma is a type of cancer that develops in epithelial cells that produce mucus or fluids. Glandsular tissues are epithelial tissues with this type of epithelial cell. Adenocarcinomas are the most common cancers of the breast, colon, and prostate.
Basal cell carcinoma is a cancer that starts in the epidermis, a person's outer layer of skin, in the lower or basal (base) layer.
Squamous cell carcinoma is a type of skin cancer that develops in squamous cells, which are epithelial cells found just beneath the skin's surface. Many other organs, such as the stomach, intestines, lungs, bladder, and kidneys, are lined with squamous cells. When viewed under a microscope, squamous cells appear flat, like fish scales. Epidermoid carcinomas are another name for squamous cell carcinomas.
Transitional cell carcinoma is a cancer that develops in the transitional epithelium, or urothelium, a type of epithelial tissue. The linings of the bladder, ureters, and part of the kidneys (renal pelvis), as well as a few other organs, are made up of many layers of epithelial cells that can get bigger and smaller. Transitional cell carcinomas are cancers of the bladder, ureters, and kidneys.
Sarcomas are cancers that develop in the soft tissues of the body, such as muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).
The most common bone cancer is osteosarcoma. Leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans are the most common soft tissue sarcomas.
Leukemias are cancers that start in the bone marrow's blood-forming tissue. Solid tumours are not formed by these cancers. In the blood and bone marrow, large numbers of abnormal white blood cells (leukaemia cells and leukemic blast cells) build up, crowding out normal blood cells. The body's ability to get oxygen to its tissues, control bleeding, and fight infections can all be hampered by a lack of normal blood cells.
Leukemia is divided into four types based on how quickly the disease progresses (acute or chronic) and the type of blood cell in which the cancer begins (lymphoblastic or myeloid). Acute leukaemia grows quickly, while chronic leukaemia grows more slowly.
Lymphoma is a type of cancer that starts in the lymphocytes (T cells or B cells). These are white blood cells that fight disease and are part of the immune system. Abnormal lymphocytes accumulate in lymph nodes and lymph vessels, as well as other organs, in lymphoma.
Lymphoma is divided into two types: non-Hodgkin lymphoma and Hodgkin lymphoma
Reed-Sternberg cells are abnormal lymphocytes that are found in people with Hodgkin lymphoma. B cells are usually the source of these cells.
Non-Hodgkin lymphoma (NHL) is a broad term for a group of cancers that begin in lymphocytes. B cells and T cells can form cancers that grow quickly or slowly.
Multiple myeloma is a cancer that starts in plasma cells, which are an immune cell type. Myeloma cells, which are abnormal plasma cells, build up in the bone marrow and cause tumours in bones all over the body. Plasma cell myeloma and Kahler disease are other names for multiple myeloma.
Melanoma is a cancer that starts in cells that develop into melanocytes, specialised cells that produce melanin (the pigment that gives skin its color). Melanomas most commonly develop on the skin, but they can also develop in other pigmented tissues, such as the eye.
BRAIN AND SPINAL CORD TUMORS
Tumors of the brain and spinal cord come in a variety of shapes and sizes. These tumours are named after the type of cell that gave rise to them and the location in the central nervous system where they first appeared. An astrocytic tumour, for example, begins in astrocytes, which are star-shaped brain cells that help keep nerve cells healthy. Brain tumours can be benign (i.e., not cancerous) or malignant (i.e., cancerous) (cancer).
OTHER TYPES OF TUMORS
GERM CELL TUMORS
Germ cell tumours are cancers that start in the cells that produce sperm or eggs. These tumours can be benign or malignant and can appear almost anywhere on the body.
Neuroendocrine tumours arise when cells in the nervous system release hormones into the bloodstream in response to a signal. These tumours, which produce higher-than-normal levels of hormones, can result in a variety of symptoms. Neuroendocrine tumours can be either benign or cancerous.
Neuroendocrine tumours, such as carcinoid tumours, are a type of neuroendocrine tumour. They are slow-growing tumours that most commonly occur in the gastrointestinal tract (most often in the rectum and small intestine). Carcinoid tumours can spread to the liver or other parts of the body, secreting chemicals like serotonin and prostaglandins, resulting in carcinoid syndrome.
New medications and treatment technologies have been developed as a result of innovative research.
Treatments are usually prescribed based on the type of cancer, its stage at the time of diagnosis, and the patient's overall health.
Here are some examples of cancer treatment approaches:
•Chemotherapy uses medications that target rapidly dividing cells to kill cancerous cells. The drugs can also help shrink tumours, but they can have serious side effects.
• Hormone therapy entails taking medications that alter the way certain hormones function or prevent the body from producing them. This is a common approach when hormones play a significant role, such as in prostate and breast cancers.
• Immunotherapy is a type of treatment that boosts the immune system and encourages it to fight cancerous cells by using medications and other treatments. Checkpoint inhibitors and adoptive cell transfer are two examples of these treatments.
• Precision medicine, also known as personalised medicine, is a relatively new concept. It entails using genetic testing to determine the most effective treatments for a person's specific cancer presentation. However, researchers have yet to demonstrate that it is effective in treating all types of cancer.
• Radiation therapy kills cancerous cells by exposing them to high doses of radiation. A doctor may also suggest that radiation be used to shrink a tumour before surgery or to alleviate tumor-related symptoms.
• People with blood-related cancers, such as leukaemia or lymphoma, may benefit from a stem cell transplant. It entails removing cells that have been destroyed by chemotherapy or radiation, such as red or white blood cells. The cells are then strengthened and reintroduced into the body by lab technicians.
• When a person has a cancerous tumour, surgery is frequently part of the treatment plan. A surgeon may also remove lymph nodes to slow or stop the disease from spreading.
•Targeted therapies prevent cancerous cells from multiplying by performing functions within them. They may also help to strengthen the immune system. Small-molecule drugs and monoclonal antibodies are two examples of these therapies.
To maximise effectiveness, doctors will frequently use more than one type of treatment.