What is cancer?


Cancer is a group of diseases that develop when cells in a part of the body begin to grow and spread out of control. If the spread is not controlled, it can result in death. Cancer is caused by both external factors (tobacco, chemicals, radiation, and infectious organisms) and internal factors (inherited mutations, hormones, immune conditions, and mutations that occur from metabolism). These causal factors may act together or in sequence to initiate or promote carcinogenesis.


Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person’s life, normal cells divide more rapidly until the person becomes an adult. After that, cells in most part of the body divide only to replace worn-out or dying cells and to repair injuries.


Because cancer cells continue to grow and divide, they are different from normal cells. Instead of dying, they outlive normal cells, and continue to form abnormal cells. Cancer cells often travel to other parts of the body where they begin to grow and replace normal tissue. This process, called metastasis, occurs as the cancer cells get into the bloodstream or lymph vessels of our body. When cells from a cancer, like breast cancer, spread to another organ like the liver, the cancer is still called breast cancer, not liver cancer.


Cancer cells develop because of damage to DNA. This substance is in every cell and directs all its activities. Most of the time when DNA becomes damaged the body is able to repair it. In cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which accounts for inherited cancers. Many times a person’s DNA becomes damaged by exposure to something in the environment, like smoking.


Cancer usually forms as a solid tumor. Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow. Not all tumors are cancerous. Benign (noncancerous) tumors do not spread to other parts of the body (metastasize) and, with rare exceptions, are not life threatening.


Different types of cancer can behave very differently. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. This is why people with cancer need treatment that is aimed at their particular kind of cancer.


Common Types of Cancer


Common types of cancer are those that are diagnosed with the greatest frequency in the United States. The most common type of cancer on this list is non-melanoma skin cancer, representing about half of all cancers diagnosed in this country. The cancer on the list with the lowest incidence is thyroid cancer.


Skin Cancer: Cancer that forms in the tissues of the skin. When cancer forms in cells that make pigment, it is called melanoma. When cancer forms in cells that do not make pigment it may begin in basal cells (small, round cells in the base of the outer layer of skin) or squamous cells (flat cells that form the surface of the skin). Both types of skin cancer usually occur in skin that has been exposed to sunlight, such as the skin on the face, neck, hands and arms. More than one million cases of basal cell or squamous cancer occur annually. Most of the forms of skin cancer are highly curable. The most serious form is melanoma.


Breast Cancer: Breast cancer is the most frequently diagnosed cancer in women. It is a cancer that forms in the tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare.


Prostate Cancer: Cancer that forms in the tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the rectum). Prostate cancer usually occurs in older men, and is the most frequently diagnosed cancer in men.


Colon Cancer: Cancer that forms in the tissues of the colon (the longest part of the large intestine). Most colon cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).


Rectal Cancer: Cancer that forms in the tissues of the rectum (the last several inches of the large intestine before the anus).


Note: Colorectal cancer (the combination of colon and rectal cancer) is the third most common cancer in both men and women.


Bladder Cancer: Cancer that forms in the tissues of the bladder (the organ that stores urine). Most bladder cancers are transitional cell carcinomas (cancer that begins in cells that normally make up the inner lining of the bladder). Other types include squamous cell carcinoma (cancer that begins in thin, flat cells) and adenocarcinoma (cancer that begins in cells that make and release mucus and other fluids). The cells that form squamous cell carcinoma and adenocarcinoma develop in the inner lining of the bladder as a result of chronic irritation and inflammation.


Lung Cancer: Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope. Lung cancer accounts for the most cancer-related deaths in both men and women. Cigarette smoking is by far the most important risk factor for lung cancer.


Melanoma: A form of skin cancer that begins in melanocytes (the cells that make the pigment melanin). Melanoma usually begins in a mole. Endometrial Cancer: Cancer that forms in the tissue lining the uterus (the small, hollow, pear-shaped organ in a woman’s pelvis in which a baby grows). Most endometrial cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).


Kidney Cancer: Cancer that forms in tissues of the kidneys. Kidney cancer includes renal cell carcinoma (cancer that forms in the lining of very small tubes in the kidney that filter the blood and remove waste products) and renal pelvis carcinoma (cancer that forms in the center of the kidney where urine collects). It also includes Wilms’ tumor, which is a type of kidney cancer that usually develops in children under the age of 5.


Leukemia: Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of blood cells to be produced and enter the bloodstream.


Non-Hodgkin Lymphoma (NHL): Any of a large group of cancers of the immune system. NHLs can occur at any age and are often marked by enlarged lymph nodes, fever, and weight loss. There are many different types of NHL, which can be divided into aggressive (fast growing) and indolent (slow growing) types and can be classified as either B-cell or T-cell NHL. B-cell NHLs include Burkitt’s lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, immunoblastic large cell lymphoma, precursor B-lymphoblastic lymphoma, and mantle cell lymphoma. T-cell NHLs include mycosis fungoides, anaplastic large cell lymphoma, and precursor T-lymphoblastic lymphoma. Lymphomas related to lymphoproliferative disorders following bone marrow or stem cell transplantation are usually B-cell NHLs. Prognosis and treatment depend on the state and type of disease.


Pancreatic Cancer: A disease in which malignant (cancer) cells are found in the tissue of the pancreas. Also called exocrine cancer.


Thyroid Cancer: Cancer that forms in the thyroid gland (an organ at the base of the throat that makes hormones that help control heart rate, blood pressure, body temperature, and weight). Four main types of thyroid cancer are papillary, follicular, medullary, and anaplastic thyroid cancer. The four types are based on how the cancer cells look under a microscope.


Signs and Symptoms of Common Cancers


Breast: The earliest sign of breast cancer is usually an abnormality detected on a mammogram before it can be felt by the woman or a health care professional. Larger tumors may become evident as a painless mass. Less common symptoms include persistent changes to the breast, such as thickening, swelling, distortion, tenderness, skin irritation, scaliness, or nipple abnormalities such as ulceration, retraction, or spontaneous discharge. Typically, breast pain results from benign conditions and is not an early symptom of breast cancer.


Colon and Rectum: Screening is necessary to detect colorectal cancer in its early stages. Advanced disease may cause rectal bleeding, blood in the stool, a change in bowel habits, and cramping pain in the lower abdomen.


Leukemia: Symptoms may include fatigue, paleness, weight loss, repeated infections, fever, bruising easily, and nosebleeds or other hemorrhages. In children, these signs can appear suddenly. Chronic leukemia can progress slowly with few symptoms.


Lung: Symptoms may include persistent cough, sputum streaked with blood, chest pain, voice change, and recurrent pneumonia or bronchitis.


Lymphoma: Symptoms may include swollen lymph nodes, itching, night sweats, fatigue, unexplained weight loss, and intermittent fever.


Ovary: The most common sign is enlargement of the abdomen, which is caused by accumulation of fluid. Abnormal vaginal bleeding occurs rarely. In women older tan 40, persistent digestive disturbances (stomach discomfort, gas, distention) may indicate the need for an evaluation for ovarian cancer. Recent research has suggested that urinary symptoms may be another sign of ovarian cancer.


Pancreas: Cancer of the pancreas often develops without early symptoms which, when present, can include weight loss, discomfort in the abdomen, and occasionally glucose intolerance. Tumors that develop near the common bile duct may cause a blockage that leads to jaundice (yellowing of the skin and eyes due to pigment accumulation). Sometimes this symptom allows the tumor to be diagnosed at an early stage.


Prostate: Early prostate cancer usually has no symptoms. With more advanced disease, individuals may experience weak or interrupted urine flow; inability to urinate or difficulty starting or stopping the urine flow; the need to urinate frequently, especially at night; blood in the urine; or pain or burning with urination. Continual pain in the lower back, pelvis, or upper thighs may be an indication of metastatic disease. Many of these symptoms, however, are similar to those caused by benign conditions.


Skin: Important warning signs of melanoma include changes in size, shape, or color of skin lesion or the appearance of a new growth on the skin. Changes that occur over a few days are generally innocuous but changes that progress over a month or more should be evaluated by your doctor. Basal cell carcinomas may appear as flat, firm, pale areas or as small, raised, pink or red, translucent, shiny areas that may bleed following minor injury. Squamous cell cancer may appear as growing lumps, often with a rough surface, or as flat, reddish patches that grow slowly. Another sign of basal and squamous cell skin cancers is a sore that doesn’t heal.


Bladder: Symptoms may include blood in the urine and increased frequency of urination.


Cervix: Symptoms usually do not appear until abnormal cervical cells become cancerous and invade nearby tissue. When this happens, the most common symptom is abnormal vaginal bleeding. Bleeding may start and stop between regular menstrual periods, or it may occur after sexual intercourse, douching, or a pelvic exam. Menstrual bleeding may last longer and be heavier than usual. Bleeding after menopause or increased vaginal discharge may also be symptoms.


Uterus: Abnormal uterine bleeding or spotting is a frequent early sign. Pain and systemic symptoms are late signs.


Early Detection Screening for Selected Cancers


Breast: Mammography can detect breast cancer at an early stage when treatment may be more effective. Studies have shown that early detection saves lives and increases treatment options. Mammography is highly accurate but like most medical tests, it is not perfect. On average, mammography will detect about 80% to 90% of breast cancers in women without symptoms. All suspicious lumps should be biopsied for a definitive diagnosis. Recent studies have shown that magnetic resonance imaging (MRI) appears to be more sensitive than mammography in detecting tumors in women with an inherited susceptibility to breast cancer.


Colon and Rectum: Beginning at age 50, men and women who are at average risk for developing colorectal cancer should begin screening. Screening can result in the detection and removal of colorectal polyps before they become cancerous as well as the detection of cancer that is at an early stage. Screening reduces the mortality both by decreasing incidence and by detecting a higher proportion of cancers at early, more treatable stages. Screening includes various blood tests; flexible sigmoidoscopy; barium enema; and colonoscopy.


Leukemia: Because symptoms often resemble those of other, less serious conditions, leukemia can be difficult to diagnose early. When a physician does suspect leukemia, diagnosis can be made using blood tests and a bone marrow biopsy.


Lung: Efforts at early detection have not yet been demonstrated to reduce mortality. Chest x-ray, analysis of cells in sputum, and fiberoptic examination of the bronchial passages have shown limited effectiveness in improving survival. Newer tests, such as low-dose spiral computed tomography (CT) scans and molecular markers in sputum, have produced promising results in detecting lung cancers at earlier, more operable stages when survival is better. However, there are considerable risks associated with lung biopsy and surgery that must be considered when evaluating the risks and benefits of screening.


Ovary: Routine screening for women at average risk is not recommended because no sufficiently accurate screening test is currently available. The pelvic examination can only occasionally detect ovarian cancer, generally when the disease is already in advanced stages. However, the combination of a thorough pelvic exam, transvaginal ultrasound, and a blood test for the tumor marker CA125 should be offered to woman who are at high risk of ovarian cancer and to women who have symptoms. For women at average risk, transvaginal ultrasound and testing for the tumor marker CA125 may help in diagnosis but are not used for routine screening.


Pancreas: At present there is no method for the early detection of pancreatic cancer and the early stages of the disease are usually asymptomatic. Researchers are focusing on ways to diagnose pancreatic cancer before symptoms occur.


Prostate: At this time, there are insufficient data to recommend for or against prostate cancer testing in men at average risk of developing the disease. The American Cancer Society recommends that beginning at age 50, the PSA blood test (which detects a protein made by the prostate called prostate-specific antigen) and the digital rectal examination should be offered to men at average risk. Individuals at high risk of developing prostate cancer (African Americans or men with a strong family history) should begin screening at age 45. All men should be given information about the benefits and limitations of testing so they can make informed decisions.


Skin: The best way to detect skin cancer early is to recognize changes in skin growths or the appearance of new growths. Adults should examine their skin regularly. Suspicious lesions or progressive changes in a lesion’s appearance or size should be evaluated promptly by a physician. Melanomas often start as small, mole-like growths that increase in size and change color. A simple ABCD rule outlines the warning signals of the most common type of melanoma: A is for asymmetry (one half of the mole does not match the other half); B is for border irregularity (the edges are ragged, notched, or blurred); C is for color (the pigmentation is not uniform, with variable degrees of tan, brown, or black); D is for diameter greater than 6 millimeters (about the size of a pencil eraser).


Bladder: Bladder cancer is diagnosed by examination of cells in the urine under a microscope and examination of the bladder wall with a cystoscope, a slender tube fitted with a lens and light that can be inserted through the urethra. These tests are not recommended for screening people at average risk but are used for people at increased risk due to occupational exposure, or for follow-up after bladder cancer treatment to detect recurrent or new tumors.


Cervix: The Pap test is a simple procedure in which a small sample of cells is collected from the cervix and examined under a microscope. Pap tests are effective but not perfect. Their results sometimes appear normal even when a woman has abnormal cells of the cervix, and likewise, sometimes appear abnormal when there are no abnormal lesions on the cervix. DNA tests to detect HPV (human papillomavirus) strains associated with cervical cancer may be used in conjunction with the Pap test, particularly when results are equivocal. Fortunately, most cervical precancers develop slowly, so nearly all cases can be prevented if a woman is screened regularly.


Uterus: Most endometrial (body and lining of the uterus) cancer is diagnosed at an early stage because of postmenopausal bleeding. Women are encouraged to report any unexpected bleeding or spotting to their physicians. Annual screening for endometrial cancer with endometrial biopsy beginning at age 35 should be offered to women with or at risk for HNPCC (hereditary nonpolyposis colon cancer).


Can Cancer Be Prevented?


According to leading medical professionals, all cancers caused by cigarette smoking and heavy use of alcohol could be prevented completely. Scientific evidence suggests that about one-third of cancer deaths are related to overweight or obesity, physical inactivity, and nutrition, and thus could also be prevented. Certain cancers are related to infectious agents, such as hepatitis B virus (HBV), human papillomavirus (HPV), human immunodeficiency virus (HIV), and others, and could be prevented through behavioral changes, vaccines, or antibiotics. In addition, many of the reported skin cancers could have been prevented by protection from the sun’s rays.


Regular screening examinations by a health care professional can result in the prevention of cervical and colorectal cancers through the discovery and removal of precancerous lesions. Screening can detect cancers of the breast, colon, rectum, cervix, prostate, oral cavity, and skin at early stages. For most of these cancers, early detection has been proven to reduce mortality. A heightened awareness of breast changes or skin changes may also result in detection of these tumors at earlier stages. Cancers that can be prevented or detected earlier by screening account for at least half of all new cancer cases. The 5-year survival rate for these cancers is about 86%, a reflection of real reductions in mortality as well as earlier diagnosis because of screening.


Who Is at Risk of Developing Cancer?


Anyone can develop cancer. The risk of being diagnosed with cancer increases as individuals grow older. Most cases occur in adults who are middle-aged or older. It is estimated that about 77% of all cancers are diagnosed in persons 55 and older.


The word risk is used in different ways by researchers, most commonly expressing risk as lifetime or relative. Lifetime risk refers to the probability that an individual, over the course of a lifetime, will develop or die from cancer. In the U.S., men have slightly less than a 1 in 2 lifetime risk for developing cancer. For women, the risk is a little more than 1 in 3.


Relative risk is a measure of the strength of the relationship between risk factors and a particular cancer. It compares the risk of developing cancer in persons with a certain exposure or trait to the risk in persons who do not have this characteristic. For example, women who have a first-degree relative (mother, sister, or daughter) with a history of breast cancer have about twice the risk of developing breast cancer compared with women who do not have a family history.


About 5% of all cancers are strongly hereditary, in that an inherited genetic alteration confers a very high risk of developing one or more specific types of cancer. However, most cancers do not result from inherited genes but from damage (mutation) to genes that occurs during one’s lifetime. Mutations may result from internal factors such as hormones or the digestion of nutrients within cells, or external factors such as tobacco, chemicals, and sunlight. 

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Cancer is a group of diseases that develop

when cells in a part of the body begin to

grow and spread out of control.​




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