Cancer is the uncontrolled growth of abnormal cells anywhere in a body. The abnormal cells are termed cancer cells, malignant cells, or tumor cells.
Many cancers and the abnormal cells that compose the cancer tissue are further identified by the name of the tissue that the abnormal cells originated from (for example, breast cancer, lung cancer, colon cancer). Cancer is not confined to humans; animals and other living organisms can get cancer.
Frequently, cancer cells can break away from this original mass of cells, travel through the blood and lymph systems, and lodge in other organs where they can again repeat the uncontrolled growth cycle. This process of cancer cells leaving an area and growing in another body area is termed metastatic spread or metastatic disease.
For example, if breast cancer cells spread to a bone (or anywhere else), it means that the individual has metastatic breast cancer.
There are over 200 types of cancers; most can fit into the following categories according to the National Cancer Institute:
Cancer that begins in the skin or in tissues that line or cover internal organs.
Cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
Lymphoma and myeloma:
Cancers that begin in the cells of the immune system.
Central nervous system cancers:
Cancers that begin in the tissues of the brain and spinal cord.
The three most common cancers in men, women and children in the U.S. are as follows:
- Men: Prostate, lung, and colorectal.
- Women: Breast, colorectal, and lung.
- Children: Leukemia, brain tumors, and lymphoma.
The incidence of cancer and cancer types are influenced by many factors such as age, sex, race, local environmental factors, diet, and genetics. Consequently, the incidence of cancer and cancer types vary depending on these variable factors.
For example, the World Health Organization (WHO) provides the following general information about cancer worldwide:
Cancer is a leading cause of death worldwide. It accounted for 7.4 million deaths (around 13% of all deaths) in 2004 (statistics published in 2009).
Lung, stomach, liver, colon, and breast cancer cause the most cancer deaths each year.
Deaths from cancer worldwide are projected to continue rising, with an estimated 12 million deaths in 2030.
Different areas of the world may have cancers that are either more or less predominant then those found in the U.S. One example is that stomach cancer is often found in Japan, while it is rarely found in the U.S.
The objective of this article is to introduce the reader to general aspects of cancers. It is designed to be an overview of cancer and cannot cover every cancer type. This article will also attempt to help guide the reader to more detailed sources about specific cancer types.
Symptoms and signs of cancer depend on the type of cancer, where it is located, and/or where the cancer cells have spread. For example, breast cancer may present as a lump in the breast or as nipple discharge while metastatic breast cancer may present with symptoms of pain (if spread to bones), extreme fatigue (lungs), or seizures (brain).
A few patients show no signs or symptoms until the cancer is far advanced. However, there are some signs and symptoms, although not specific, which usually occur in most cancer patients that are fairly easy for the person to detect.
They are as follows:
- Fever (no clear infectious source, recurrent or constant).
- Fatigue (not relived by rest).
- Weight loss (without trying to lose weight).
- Pain (usually persistent).
- Skin changes (coloration, sores that do not heal, white spots in mouth or on tongue, wart changes).
- Change in bowel or bladder functions (including trouble swallowing orconstipation).
- Unusual bleeding (mouth, vaginal, and bladder) or discharge.
- Persistent cough or change in voice.
- Lumps or tissue masses.
Anyone with these signs and symptoms should consult their doctor.
Many cancers will present with some of the above general symptoms but often have one or more symptoms that are more specific for the cancer type. For example, lung cancer may present with common symptoms of pain, but usually the pain is located in the chest. The patient may have unusual bleeding, but the bleeding usually occurs when the patient coughs. Lung cancer patients often become short of breath, and then become very fatigued.
Because there are so many cancer types (see next section) with so many nonspecific and sometimes more specific symptoms, the best way to learn about signs and symptoms of specific cancer types is to spend a few moments researching symptoms of a specific body area in question.
Conversely, a specific body area can be searched to discover what signs and symptoms a person should look for in that area that is suspected of having cancer.
However, your own research should not replace consulting a health-care provider if you ae concerned about cancer.
Anything that may cause a normal body cell to develop abnormally potentially can cause cancer. Many things can cause cell abnormalities and have been linked to cancer development. Some cancer causes remain unknown while other cancers may develop from more than one known cause. Some may be developmentally influenced by a person's genetic makeup.
Many patients develop cancer due to a combination of these factors. Although it is often difficult or impossible to determine the initiating event(s) that cause a cancer to develop in a specific person, research has provided clinicians with a number of likely causes that alone or in concert with other causes, are the likely candidates for initiating cancer.
The following is a listing of major causes and is not all-inclusive as specific causes are routinely added as research advances:
Chemical or toxic compound exposures:
Benzene, asbestos, nickel, cadmium, vinyl chloride, benzidine, N-nitrosamines, tobacco or cigarette smoke (contains at least 66 known potential carcinogenic chemicals and toxins), and aflatoxin.
Uranium, radon, ultraviolet rays from sunlight, radiation from alpha, beta, gamma, and X-ray-emitting sources.
Human papillomavirus (HPV), EBV or Epstein-Barr virus, hepatitis viruses B and C, Kaposi's sarcoma-associated herpesvirus (KSHV), Merkel cell polyomavirus, Schistosoma spp., and Helicobacter pylori; other bacteria are being researched as possible agents.
A number of specific cancers have been linked to human genes and are as follows: breast, ovarian, colorectal, prostate, skin and melanoma; the specific genes and other details are beyond the scope of this general article. It is important to point out that most everyone is exposed to cancer-causing substances (for example, sunlight, cigarette smoke, and X-rays) during their lifetime but many individuals do not develop cancer.
In addition, many people have the genes that are linked to cancer but do not develop it. Why? Although researchers may not be able give a satisfactory answer for every individual, it is clear that the higher the amount or level of cancer-causing materials a person is exposed to, the higher the chance the person will develop cancer. In addition, the people with genetic links to cancer may not develop it for similar reasons (lack of enough stimulus to make the genes function).
In addition, some people may have a heightened immune response that controls or eliminates cells that are or potentially may become cancer cells.
There is evidence that even certain dietary lifestyles may play a significant role in conjunction with the immune system to allow or prevent cancer cell survival. For these reasons, it is difficult to assign a specific cause of cancer to many individuals.
Proving that a substance does not cause or is not related to increased cancer risk is difficult. For example, antiperspirants are considered to possibly be related to breast cancer by some investigators and not by others.
The official stance by the NCI is "additional research is needed to investigate this relationship and other factors that may be involved". This unsatisfying conclusion is presented because the data collected so far is contradictive.
Other claims that are similar require intense and expensive research which may never be done. Reasonable advice might be to avoid large amounts of any compounds even remotely linked to cancer, although it may be difficult to do in complex, technologically advanced modern societies.
The treatment for cancer is usually designed by a team of doctors or by the patient's oncologist and is based on the type of cancer and the stage of the cancer. Most treatments are designed specifically for each individual. In some people, diagnosis and treatment may occur at the same time if the cancer is entirely surgically removed when the surgeon removes the tissue for biopsy.
Although patients may obtain a unique treatment protocol for their cancer, most treatments have one or more of the following components: surgery, chemotherapy, radiation therapy, or combination treatments (a combination of two or all three treatments).
Individuals obtain variations of these treatments for cancer. Patients with cancers that cannot be cured (completely removed) by surgery usually will get combination therapy, the composition determined by the cancer type and stage.
Palliative therapy (medical care or treatment used to reduce disease symptoms but unable to cure the patient) utilizes the same treatments described above. It is done with the intent to extend and improve the quality of life of the terminally ill cancer patient. There are many other palliative treatments to reduce symptoms such as pain medications and antinausea medications.