Cancer is an abnormal growth of cells. Cancer cells quickly reproduce event without enough space and nutrients. They also grow despite signals sent from the body to stop reproduction. Cancer cells are often shaped differently from healthy cells. They do not work well and can spread to many parts of the body. Tumors, masses, or lesions are names for abnormal growths of tissue that can become cancer. Their growth is not regulated.
Oncology is the branch of medicine that studies the diagnosis and treatment of cancer.
Tumors can be benign (noncancerous) or malignant (cancerous). Benign tumors tend to grow slowly and do not spread. Malignant tumors can grow quickly. They invade and destroy nearby normal tissues and spread throughout the body.
Cancer is malignant because it can be locally invasive and metastatic:
Locally invasive. The tumor can invade the tissues surrounding it by sending out "fingers" of cancerous cells into the normal tissue.
Metastatic. The tumor can send cells into other tissues in the body. These may be far from the original tumor.
The original tumor is called the primary tumor. Its cells, which can break off and travel through the body, can start to form new tumors in other organs. These new tumors are called secondary tumors. The cancerous cells travel through your blood – the circulatory system – or lymphatic system to form secondary tumors. The lymphatic system is a series of small vessels that collect waste from cells. It carries it into larger vessels, and finally into lymph nodes. Lymph fluid eventually drains into your bloodstream.
Cancer is named after the part of the body where it first started. When cancer spreads, it keeps this same name. For instance, if kidney cancer spreads to your lungs, it’s still kidney cancer, not lung cancer. (The cancer in the lung would be an example of a secondary tumor.)
Staging is the process of figuring out if cancer has spread and, if so, how far. More than one system is used for staging cancer. The definition of each stage depends on the type of cancer.
Cancer is not just one disease. Rather, it’s a group of diseases, all of which cause cells in the body to change and grow out of control. Cancers are classified by the kind of fluid or tissue from which they come from. Or they can be classified due to the location in the body where they first started. Some cancers are of mixed types. These categories are the tissue and blood classifications of cancer:
Carcinoma. A carcinoma is a cancer found in body tissue called epithelial tissue. It covers or lines surfaces of organs, glands, or body structures. For instance, a cancer of the lining of the stomach is called a carcinoma. The two most common types of carcinomas are include squamous and adenocarcinomas. Many carcinomas affect organs or glands that are involved with secretion. These include breasts that make milk. Carcinomas account for 80% to 90% of all cancers.
Sarcoma. A sarcoma is a malignant tumor growing from connective tissues. These can include cartilage, fat, muscle, tendons, and bones. The most common sarcoma, a tumor on the bone, usually occurs in young adults. Examples include osteosarcoma (bone) and chondrosarcoma (cartilage).
Lymphoma. Lymphoma is a cancer that starts in the nodes or glands of the lymphatic system. The lymphatic system makes white blood cells and cleans body fluids. Some lymphomas start in lymph tissue in organs. These include the brain or stomach. Lymphomas are classified into two categories: Hodgkin lymphoma and non-Hodgkin lymphoma.
Leukemia. Leukemia is also known as blood cancer. It’s a cancer of the bone marrow that keeps the marrow from making normal red and white blood cells and platelets. White blood cells are needed to fight infections. Red blood cells are needed to prevent anemia. Platelets keep the body from bruising and bleeding easily. Examples include acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphocytic leukemia, and chronic lymphocytic leukemia. The terms myelogenous and lymphocytic indicate the type of cells that are involved.
Myeloma. Myeloma grows in the plasma cells of bone marrow. In some cases, the myeloma cells collect in one bone and form a single tumor. This is called a plasmacytoma. However, in other cases, the myeloma cells collect in many bones, forming many tumors. This is called multiple myeloma.
Cancer has no single cause. Experts think that it’s the interaction of many factors that leads to cancer. The factors may be genetic, environmental, or lifestyle characteristics.
Some cancers have been linked with certain risk factors. A risk factor is anything that may increase your chance of getting a disease. A risk factor does not necessarily cause the disease, but it may mean you’re more likely to get it.
People with an increased risk of cancer can reduce their risk by keeping up with screenings. Reducing certain risk factors can also help. Cancer treatment tends to work better when the cancer is found early. Risk factors of cancer include:
Lifestyle factors. These include smoking, a high-fat diet, and exposure to ultraviolet light (UV radiation from the sun). These are only risk factors for adult cancers. Most children with cancer are too young to have been exposed to lifestyle factors long-term.
Genetic factors. Family history, inheritance, and genetics may play a role in some cancers. Some cancers run in families. Some gene alterations are inherited. However, this does not mean that the person will get cancer. It just means that the chance of getting cancer is higher. It isn’t known if the disease is caused by a genetic mutation, other factors, or a coincidence.
Virus exposure. Exposures to certain viruses have been linked to cancer. These include the human papillomavirus (HPV) and HIV, the virus that causes AIDS. These viruses may change your cells in some way. Over time, these changes may become a cancer cell that makes more cancer cells. Cancer isn’t contagious. You cannot get it from another person.
Environmental factors. People with certain jobs, such as painters, farmers, construction workers, and those in the chemical industry, seem to have a higher risk of some cancers. This is likely due to exposures to certain chemicals. Other environmental factors in your home may also be linked to cancer. These can include radon, a radioactive gas.
Certain genes contribute to cancer. Almost all cancers have some type of genetic alteration. A small percentage of these alterations are inherited. But the rest happen by chance.
Three main types of genes can affect cell growth. They are altered, or mutated, in certain types of cancers. These include:
Oncogenes. These genes control the normal growth of cells. Scientists say oncogenes are like a cancer "switch" that most people have in their bodies. It isn’t known what "flips the switch" to make abnormal cancer cells grow, though.
Tumor suppressor genes. These genes are able to spot abnormal growth and reproduction of damaged cells, or cancer cells. They can interrupt their reproduction. But if the tumor suppressor genes are mutated and don’t work well, cancer may grow.
Mismatch-repair genes. These genes help find errors when DNA is copied to make a new cell. If the DNA does not "match" perfectly, these genes repair the mismatch and correct the error. If these genes aren’t working well, however, errors in DNA can travel to new cells. This causes them to be damaged.
In most cases, the number of cells in our body tissues is tightly controlled. New cells are made for normal growth and development. They also replace dying cells. Cancer is a loss of this balance. It occurs due to genetic changes that "tip the balance" in favor of excessive cell growth.
Diagnosis, treatment, and prognosis for childhood cancers are different than for adult cancers. The main differences are the survival rate and the cause of the cancer. The five-year survival rate for childhood cancer is about 83%. The five-year survival rate for adult cancers is about 68%. This may be because childhood cancer responds better to treatment. Plus, a child can tolerate more aggressive treatment.
Childhood cancers often occur in the stem cells. These are simple cells that make other types of specialized cells that the body needs. A cell change that occurs by chance is often what causes childhood cancer. In adults, the type of cell that becomes cancerous is usually an epithelial cell. This is one of the cells that line the body cavity and cover the body surface. These include the surfaces of organs, glands, or body structures. Cancer in adults usually occurs from environmental exposures to these cells over time. Adult cancers are sometimes called as acquired for this reason.
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