The term cancer refers to many different diseases. They all have in common uncontrolled cell proliferation (growth and division). Cancers are usually named for the organ or cell type that is originally involved. After beginning at one site, the cancerous cells may metastasize (spread) to other organs and then continue to grow, causing more damage in the new location as well. The cancer is still named by its place of origin.
All known carcinogens (cancer-inducing agents), which include various chemicals, viruses, and ionizing radiation, act by breaking chemical bonds to produce DNA mutations.  These mutations occur randomly throughout the genome, and if not repaired by the cell's DNA repair mechanisms, they can impede normal cellular functions. If enough unrepaired mutations occur in genes associated with cell growth, this can cause the cells to grow when they should not.
Types of Cancer
Data are for USA
- Most common cancers in men:
- Deadliest cancers in men:
- Most common cancers in women
- Deadliest cancers in women
Prevention and Screening
Preventative strategies are continuously being revised. Please see references below for up to date information.
- Breast cancer: In women without a family history of breast cancer, mammograms should be done yearly. Clinical breast exam by a medical professional should also be done yearly. Women who have had abortions are significantly more likely to contract breast cancer.
- Lung cancer: There are no currently accepted preventative guidelines
- Prostate cancer: evidence is inconclusive, but most doctors recommend yearly PSA blood test and digital rectal exam
- Colon cancer: in people without a family history of colon cancer, most sources recommend a colonoscopy at age 50, with further studies based on the results. Fecal occult blood testing should also be conducted yearly.
- Cervical cancer: yearly Pap smears should be done on all women who have been sexually active and have not had a hysterectomy. Over age 65, women in monogamous relationships and recent normal Pap smears probably do not need to be screened as frequently.
- Testicular cancer: the evidence is unclear, however most physicians recommend routine testicular exams in young men.
- Skin cancer: keep skin protected from sunlight by use of clothing and sunscreen, and watch you skin for new moles, or changes in existing moles.
Treatment of cancer
Cancer treatment requires destruction or removal of cancerous cells with minimal effect to healthy cells. Since the cancerous cells are descended from healthy cells and are thus very similar to them, this is very difficult. Furthermore, the small differences are dependent on what mutations initially caused the cancer in the first place, so most treatments are only effective against a certain percentage of cancers from any one tissue.
Chemotherapy is the use of drugs that kill tumor cells. Conventionally, the drugs that are used are those that target cells which are rapidly undergoing mitosis; this approach is effective but is limited by side effects, which occur because these drugs have an adverse effect on normal tissues that contain rapidly-dividing cells. Research is under way to find drugs with a wider therapeutic index. One approach is to study specific molecular markers that may be used to identify cancer cells, and to develop drugs that preferentially kill cells that exhibit those markers.
An example of chemotherapy is dichloroacetate (DCA), a chemical with the formula: CHCl₂COOH. DCA cures cancer by restoring the mitochondria of cancer cells. Cancer cells use glycolysis to produce energy since the mitochondria is damaged and there is not enough oxygen (see. Hypoxia) to go through respiration (oxidative phosphorylation). Usually cells with a critical amount of damage (such as in cancer cells) kill themselves by apoptosis which requires properly functioning mitochondria. DCA restores the function of the mitochondria and thus apoptosis is restored. Cancer cells then begin killing themselves off.
DCA is available for purchase from websites and physicians, although it is still in the human testing trials in Canada. The trials have proved promising, but this off-label use of DCA to treat cancer has sparked lots of controversy. Most chemotherapy treatments are not so controversial, since they have undergone much more testing to guarantee their safety.
Radiation therapy involves the use of precisely-targeted radiation to destroy cancer cells. Because radiation damages DNA and thus has the ability both to treat and to cause cancer, this method of treatment must be administered by physicians highly-skilled in physics.
The goal of cancer surgery is to physically remove the abnormal cells. This becomes more difficult after the cancer spreads. Often, chemotherapy is used either before or after surgery to kill cancer cells that have metastasized.
The immune system contains a number of cell types, such as NK cells and killer T cells that have the capability to destroy other cells that have become infected with viruses or have become cancerous. Immunotherapy involves the enhancement or potentiation of these natural defenses against tumor cells. This is useful because some cancer cells may have mutations that make it hard for the immune system to recognize them as abnormal. A common procedure is to remove immature immune cells from the patient's bone marrow, purify the T-cells and expose them to antigens from the tumor. The activated cells are then re-injected, allowing them to seek out cancerous tissues.
- Xu R, Pelicano H, Zhou Y, Carew J, Feng L, Bhalla K, Keating M, Huang P (2005). "Inhibition of glycolysis in cancer cells: a novel strategy to overcome drug resistance associated with mitochondrial respiratory defect and hypoxia". Cancer Res 65 (2): 613–21. PMID 15695406.
- American Cancer Society: Cancer statistics for 2007
- American Cancer Society: What is chemotherapy?
- American Cancer Society: How does chemotherapy Work?
- American Cancer Society: What's new in chemotherapy research?
- Agency for Healthcare Research and Quality: Guide to Clinical Preventive Services
- Mayo Clinic: Chemotherapy: Drug treatment uses chemicals to kill cancer cells
- Myth: Cancer cannot be prevented