Cancer 2nd post

List of contents

Contents

  

• 1Definitions
• 2Signs and symptoms
  • 2.1Local effects
  • 2.2Systemic symptoms
  • 2.3Metastasis
• 3Causes
  • 3.1Chemicals
  • 3.2Diet and exercise
  • 3.3Infection
  • 3.4Radiation
  • 3.5Heredity
  • 3.6Physical agents
  • 3.7Hormones
• 4Pathophysiology
  • 4.1Genetics
  • 4.2Epigenetics
  • 4.3Metastasis
• 5Diagnosis
  • 5.1Classification
  • 5.2Pathology
• 6Prevention
  • 6.1Dietary
  • 6.2Medication
  • 6.3Vaccination
• 7Screening
  • 7.1Recommendations
  • 7.2Genetic testing
• 8Management
  • 8.1Chemotherapy
  • 8.2Radiation
  • 8.3Surgery
  • 8.4Palliative care
  • 8.5Immunotherapy
  • 8.6Alternative medicine
• 9Prognosis
• 10Epidemiology
• 11History
• 12Society and culture
  • 12.1Economic effect
• 13Research
• 14Pregnancy
• 15Other animals
• 16Notes
• 17Further reading
• 18External links

Definitions

Cancers are a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body.^[1][2] They form a subset of neoplasms. A neoplasm or tumor is a group of cells that have undergone unregulated growth, and will often form a mass or lump, but may be distributed diffusely.^[21][22]

All tumor cells show the six hallmarks of cancer. These are characteristics that the cancer cells need to produce a malignant tumor. They include:^[23]

• Cell growth and division without the proper signals to do so
• Continuous growth and division even when there are signals telling them to stop
• Avoidance of programmed cell death
• Limitless number of cell divisions
• Promoting blood vessel construction
• Invasion of tissue and formation of metastases^[24]

The progression from normal cells to cells that can form a detectable mass to outright cancer involves multiple steps known as malignant progression.^[24][25]

Signs and symptoms

Main article: Cancer signs and symptoms

Symptoms of cancer metastasisdepend on the location of the tumor.

When cancer begins, it invariably produces no symptoms. Signs and symptoms only appear as the mass continues to grow or ulcerates. The findings that result depend on the type and location of the cancer. Few symptoms are specific, with many of them also frequently occurring in individuals who have other conditions. Cancer is the new "great imitator". Thus, it is not uncommon for people diagnosed with cancer to have been treated for other diseases, which were assumed to be causing their symptoms.^[26]

Local effects

Local symptoms may occur due to the mass of the tumor or its ulceration. For example, mass effects from lung cancer can cause blockage of the bronchusresulting in cough or pneumonia; esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow; and colorectal cancer may lead to narrowing or blockages in the bowel, resulting in changes in bowel habits. Masses in breasts or testicles may be easily felt. Ulceration can cause bleeding that, if it occurs in the lung, will lead to coughing up blood, in the bowels to anemia orrectal bleeding, in the bladder to blood in the urine, and in the uterus to vaginal bleeding. Although localized pain may occur in advanced cancer, the initial swelling is usually painless. Some cancers can cause a buildup of fluid within the chest or abdomen.^[26]

Systemic symptoms

General symptoms occur due to distant effects of the cancer that are not related to direct or metastatic spread. These may include: unintentional weight loss, fever, being excessively tired, and changes to the skin.^[27] Hodgkin disease, leukemias, and cancers of the liver or kidney can cause a persistent fever of unknown origin.^[26]

Some cancers may cause specific groups of systemic symptoms, termed paraneoplastic phenomena. Examples include the appearance of myasthenia gravis in thymoma and clubbing in lung cancer.^[26]

Metastasis

Main article: Metastasis

Cancer can spread from its original site by local spread, lymphatic spread to regional lymph nodes or by blood (haematogenous spread) to distant sites, known as metastasis. When cancer spreads by a haematogenous route, it usually spreads all over the body. However, cancer 'seeds' grow in certain selected site only ('soil') as hypothesized in the soil and seed hypothesis of cancer metastasis. The symptoms of metastatic cancers depend on the location of the tumor, and can include enlarged lymph nodes (which can be felt or sometimes seen under the skin and are typically hard), enlarged liver orenlarged spleen, which can be felt in the abdomen, pain or fracture of affected bones, and neurological symptoms.^[26]

Causes

Main article: Causes of cancer

The great majority of cancers, some 90–95% of cases, are due to environmental factors. The remaining 5–10% are due toinherited genetics.^[5] Environmental, as used by cancer researchers, means any cause that is not inherited genetically, such as lifestyle, economic and behavioral factors, and not merely pollution.^[28] Common environmental factors that contribute to cancer death include tobacco (25–30%), diet and obesity (30–35%), infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), stress, lack of physical activity, and environmental pollutants.^[5]

It is nearly impossible to prove what caused a cancer in any individual, because most cancers have multiple possible causes. For example, if a person who uses tobacco heavily develops lung cancer, then it was probably caused by the tobacco use, but since everyone has a small chance of developing lung cancer as a result of air pollution or radiation, then there is a small chance that the cancer developed because of air pollution or radiation. Excepting the rare transmissions that occur with pregnancies and only a marginal few organ donors, cancer is generally not a transmissible disease.^[29]

Chemicals

Further information: Alcohol and cancer and Smoking and cancer

The incidence of lung cancer is highly correlated with smoking.

Exposure to particular substances have been linked to specific types of cancer. These substances are called carcinogens. Tobacco smoking, for example, causes 90% of lung cancer.^[30] It also causes cancer in the larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas.^[31] Tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.^[32] Tobacco is responsible for about one in three of all cancer deaths in the developed world,^[33] and about one in five worldwide.^[32] Lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking rates since the 1950s followed by decreases in lung cancer death rates in men since 1990.^[34][35]

In Western Europe, 10% of cancers in males and 3% of all cancers in females are attributed to alcohol exposure, especially cancer of the liver and of the digestive tract.^[36] Cancer related to substance exposures at work is believed to represent between 2–20% of all cases.^[37] Every year, at least 200,000 people die worldwide from cancer related to their workplaces.^[38] Millions of workers run the risk of developing cancers such as lung cancer and mesothelioma from inhaling tobacco smoke or asbestos fibers on the job, orleukemia from exposure to benzene at their workplaces.^[38]