What is cancer?
Cancer is a broad term. It describes the disease that results when cellular changes cause the uncontrolled growth and division of cells.
Some types of cancer cause rapid cell growth, while others cause cells to grow and divide at a slower rate.
Certain forms of cancer result in visible growths called tumors, while others, such as leukemia, do not.
Most of the body’s cells have specific functions and fixed lifespans. Cell death is part of a natural and beneficial phenomenon, which healthcare professionals call apoptosis.
A cell receives instructions to die so that the body can replace it with a newer cell that functions better. Cancerous cells lack the components that instruct them to stop dividing and to die.
As a result, they build up in the body, using oxygen and nutrients that would usually nourish other cells. Cancerous cells can form tumors, impair the immune system and cause other changes that prevent the body from functioning regularly.
Cancerous cells may appear in one area, then spread via the lymph nodes. These are clusters of immune cells located throughout the body.
Causes
There are many causes of cancer, and some are preventable.
Risk factors
Preventable risk factors for cancer include:
- Smoking
- Heavy alcohol consumption
- Excess body weight
- Physical inactivity
- Poor nutrition
- Human papillomavirus infection
Other risk factors for cancer are not preventable. Currently, the most significant unpreventable risk factor is age. According to the American Cancer Society (ACS), doctors in the United States diagnose 88% of cancer cases in people ages 50 years or older.
Is cancer genetic?
Genetic factors can contribute to the development of cancer.
A person’s genetic code tells their cells when to divide and expire. Changes in the genes can lead to faulty instructions, and cancer can result.
Genes also influence the cells’ production of proteins, and proteins carry many of the instructions for cellular growth and division.
Some genes change proteins that would usually repair damaged cells. This can lead to a predisposition for cancer. If a parent has these genes, they may pass on the altered instructions to their offspring. A doctor may refer to this as an inherited gene mutation. These mutations may contribute to the development of up to 10% of cancer cases.
Some genetic mutations that increase the risk of developing cancer occur after birth. Healthcare professionals refer to these changes as “acquired gene mutations”. Possible causes include smoking and sun exposure. These genetic changes cause cancer more commonly than inherited gene mutations.
Other changes that can result in cancer take place in the chemical signals that determine how the cells turn specific genes on and off. Doctors may call these “epigenetic changes”.
Treatments
Doctors usually prescribe treatments based on the type of cancer, its stage at diagnosis, and the person’s overall health.
Some examples of cancer treatment include :
Chemotherapy aims to kill cancerous cells with medications that target rapidly dividing cells. The drugs can also help shrink tumors, but the side effects can be severe.
Hormone therapy involves taking medications that change how certain hormones work or interfere with the body’s ability to produce them. When hormones play a significant role, as with prostate and breast cancers, this is a common approach.
Immunotherapy uses medications and other treatments to boost the immune system and encourage it to fight cancerous cells.
Radiation therapy uses high-dose radiation to kill cancerous cells. Also, a doctor may recommend using radiation to shrink a tumor before surgery or reduce tumor-related symptoms.
Stem cell transplant can be especially beneficial for people with blood-related cancers, such as leukemia or lymphoma. It involves removing cells, such as red or white blood cells, that chemotherapy or radiation has destroyed. Lab technicians then strengthen the cells and put them back into the body.
Surgery is often a part of a treatment plan when a person has a cancerous tumor. Also, a surgeon may remove lymph nodes to reduce or prevent the disease’s spread.
Targeted therapies perform functions within cancerous cells to prevent them from multiplying. They can also boost the immune system. Two examples of these therapies are small-molecule drugs and monoclonal antibodies.
Doctors will often employ more than one type of treatment to maximize effectiveness.
Types
The most common type of of cancer in the U.S. is breast cancer, followed by lung and prostate cancers, according to the National Cancer Institute, which excluded nonmelanoma skin cancers from these findings.
Each year, more than 40,000 people in the country receive a diagnosis of one of the following types of cancer:
- Bladder
- Colon and rectal
- Endometrial
- Kidney
- Leukemia
- Liver
- Melanoma
- Non-Hodgkin’s lymphoma
- Pancreatic
- Thyroid
Carcinoma
Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope.
Carcinomas that begin in different epithelial cell types have specific names:
Adenocarcinoma is a cancer that forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Most cancers of the breast, colon, and prostate are adenocarcinomas.
Basal cell carcinoma is a cancer that begins in the lower or basal (base) layer of the epidermis, which is a person’s outer layer of skin.
Squamous cell carcinoma is a cancer that forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys. Squamous cells look flat, like fish scales, when viewed under a microscope. Squamous cell carcinomas are sometimes called epidermoid carcinomas.
Transitional cell carcinoma is a cancer that forms in a type of epithelial tissue called transitional epithelium, or urothelium. This tissue, which is made up of many layers of epithelial cells that can get bigger and smaller, is found in the linings of the bladder, ureters, and part of the kidneys (renal pelvis), and a few other organs. Some cancers of the bladder, ureters, and kidneys are transitional cell carcinomas.
Sarcoma
Soft tissue sarcoma forms in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints.
Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).
Osteosarcoma is the most common cancer of bone. The most common types of soft tissue sarcoma are leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans.
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 leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections.
There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell the cancer starts in (lymphoblastic or myeloid). Acute forms of leukemia grow quickly and chronic forms grow more slowly.
Lymphoma
Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.
There are two main types of lymphoma:
Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells.
Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.
Multiple Myeloma
Multiple myeloma is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myeloma is also called plasma cell myeloma and Kahler disease.
Melanoma
Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.
Brain and Spinal Cord Tumors
There are different types of brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer).
Other Types of Tumors
Germ Cell Tumors
Germ cell tumors are a type of tumor that begins in the cells that give rise to sperm or eggs. These tumors can occur almost anywhere in the body and can be either benign or malignant.
Neuroendocrine Tumors
Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system. These tumors, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.
Carcinoid Tumors
Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most often in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome.
Cancer development and cell division
Doctors classify cancer by its location in the body and the tissues that it forms in.
For example, sarcomas develop in bones or soft tissues, while carcinomas form in cells that cover internal or external surfaces in the body. Basal cell carcinomas develop in the skin, while adenocarcinomas can form in the glands.
When cancerous cells spread to other parts of the body, the medical term for this is metastasis.
A person can also have more than one type of cancer at a time.
When Cancer Spreads
In metastasis, cancer cells break away from where they first formed and form new tumors in other parts of the body.
A cancer that has spread from the place where it first formed to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer. For example, breast cancer that forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
In some cases, treatment may help prolong the lives of people with metastatic cancer. In other cases, the primary goal of treatment for metastatic cancer is to control the growth of the cancer or to relieve symptoms it is causing. Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.
Outlook
Improvements in cancer detection, increased awareness of the risks of smoking, and a drop in tobacco use have all contributed to a year-on-year decrease in the number of cancer diagnoses and deaths.
According to the ACS, the overall cancer death rate declined by 33% between 1991 and 2020.
When a person has cancer, their outlook will depend on whether the disease has spread and on its type, severity, and location.
Frequently asked questions
Below are some common questions and answers about cancer.
How do I recognize cancer before it starts to cause serious health problems?
Some cancers cause early symptoms, but others do not exhibit symptoms until they are more advanced. Many of these symptoms are often from causes unrelated to cancer.
The best way to identify cancer early is to report any unusual, persistent symptoms to a doctor so they can offer advice about any further testing that may be needed.
Can people with cancer live a long life?
Each individual’s outlook varies depending on the type of cancer they have and other factors, such as their overall health and whether the disease has spread.
However, the ACS indicates that the overall cancer death rate has declined by 33% between 1991 and 2020.
How long can someone live with cancer without knowing?
Some types of cancer do not cause symptoms in the early stages. Therefore, a person may not know they are living with the disease until it reaches more advanced stages.
For example, research indicates that carcinoid tumors may not present with any symptoms for years.
Summary
Cancer causes cells to divide uncontrollably. It also prevents them from dying at the natural point in their life cycle.
Genetic factors and lifestyle choices, such as smoking, can contribute to the development of the disease. Several elements affect the ways that DNA communicates with cells and directs their division and death.
After nonmelanoma skin cancer, breast cancer is the most common type in the U.S.
Treatments are constantly improving. Examples of current methods include chemotherapy, radiation therapy, and surgery. Some people benefit from newer options, such as stem cell transplantation and precision medicine.
The diagnosis and death rates of cancer are dropping yearly.
