Prevention
Main article: Cancer prevention
Cancer prevention is defined as active measures to decrease the risk of cancer.[85] The vast majority of cancer cases are due to environmental risk factors, and many, but not all, of these environmental factors are controllable lifestyle choices. Thus, cancer is considered a largely preventable disease.[86] Greater than 30% of cancer deaths could be prevented by avoiding risk factors including: tobacco, overweight / obesity, an insufficient diet, physical inactivity, alcohol, sexually transmitted infections, and air pollution.[87] Not all environmental causes are controllable, such as naturally occurring background radiation, and other cases of cancer are caused through hereditary genetic disorders, and thus it is not possible to prevent all cases of cancer.
Dietary
Main article: Diet and cancer
While many dietary recommendations have been proposed to reduce the risk of cancer, the evidence to support them is not definitive.[9][88] The primary dietary factors that increase risk are obesity and alcohol consumption; with a diet low in fruits and vegetables and high in red meat being implicated but not confirmed.[89][90] A 2014 meta-analysis did not find a relationship between fruits and vegetables and cancer.[91] Consumption of coffee is associated with a reduced risk of liver cancer.[92] Studies have linked excessive consumption of red or processed meat to an increased risk of breast cancer, colon cancer, and pancreatic cancer, a phenomenon that could be due to the presence of carcinogens in meats cooked at high temperatures.[93][94] Dietary recommendations for cancer prevention typically include an emphasis on vegetables, fruit, whole grains, and fish, and an avoidance of processed and red meat (beef, pork, lamb), animal fats, and refined carbohydrates.[9][88]
Medication
The concept that medications can be used to prevent cancer is attractive, and evidence supports their use in a few defined circumstances.[95] In the general population, NSAIDsreduce the risk of colorectal cancer, however due to the cardiovascular and gastrointestinal side effects they cause overall harm when used for prevention.[96] Aspirin has been found to reduce the risk of death from cancer by about 7%.[97] COX-2 inhibitor may decrease the rate of polyp formation in people with familial adenomatous polyposis, however it is associated with the same adverse effects as NSAIDs.[98] Daily use of tamoxifen or raloxifene has been demonstrated to reduce the risk of developing breast cancer in high-risk women.[99] The benefit versus harm for 5-alpha-reductase inhibitor such as finasteride is not clear.[100]
Vitamins have not been found to be effective at preventing cancer,[101] although low blood levels of vitamin D are correlated with increased cancer risk.[102][103] Whether this relationship is causal and vitamin D supplementation is protective is not determined.[104] Beta-Carotene supplementation has been found to increase lung cancer rates in those who are high risk.[105] Folic acid supplementation has not been found effective in preventing colon cancer and may increase colon polyps.[106] It is unclear if selenium supplementation has an effect.[107]
Vaccination
Vaccines have been developed that prevent infection by some carcinogenic viruses.[108] Human papillomavirus vaccine (Gardasil and Cervarix) decreases the risk of developingcervical cancer.[108] The hepatitis B vaccine prevents infection with hepatitis B virus and thus decreases the risk of liver cancer.[108] The administration of human papillomavirus and hepatitis B vaccinations is recommended when resources allow.[109]
Screening
Main article: Cancer screening
Unlike diagnosis efforts prompted by symptoms and medical signs, cancer screening involves efforts to detect cancer after it has formed, but before any noticeable symptoms appear.[110] This may involve physical examination, blood or urine tests, or medical imaging.[110]
Cancer screening is currently not possible for many types of cancers, and even when tests are available, they may not be recommended for everyone. Universal screening ormass screening involves screening everyone.[111] Selective screening identifies people who are known to be at higher risk of developing cancer, such as people with a family history of cancer.[111] Several factors are considered to determine whether the benefits of screening outweigh the risks and the costs of screening.[110] These factors include:
- Possible harms from the screening test: for example, X-ray images involve exposure to potentially harmful ionizing radiation.
- The likelihood of the test correctly identifying cancer.
- The likelihood of cancer being present: Screening is not normally useful for rare cancers.
- Possible harms from follow-up procedures.
- Whether suitable treatment is available.
- Whether early detection improves treatment outcomes.
- Whether the cancer will ever need treatment.
- Whether the test is acceptable to the people: If a screening test is too burdensome (for example, being extremely painful), then people will refuse to participate.[111]
- Cost of the test.
Recommendations
The U.S. Preventive Services Task Force (USPSTF) strongly recommends cervical cancer screening in women who are sexually active and have a cervix at least until the age of 65.[112] They recommend that Americans be screened for colorectal cancer via fecal occult blood testing, sigmoidoscopy, or colonoscopy starting at age 50 until age 75.[113]There is insufficient evidence to recommend for or against screening for skin cancer,[114] oral cancer,[115] lung cancer,[116] or prostate cancer in men under 75.[117] Routine screening is not recommended for bladder cancer,[118] testicular cancer,[119] ovarian cancer,[120] pancreatic cancer,[121] or prostate cancer.[122]
The USPSTF recommends mammography for breast cancer screening every two years for those 50–74 years old; however, they do not recommend either breast self-examination or clinical breast examination.[123] A 2011 Cochrane review came to slightly different conclusions with respect to breast cancer screening stating that routine mammography may do more harm than good.[124]
Genetic testing
See also: Cancer syndrome
| Gene | Cancer types |
|---|---|
| BRCA1, BRCA2 | Breast, ovarian, pancreatic |
| HNPCC, MLH1, MSH2, MSH6, PMS1, PMS2 | Colon, uterine, small bowel, stomach, urinary tract |
Genetic testing for individuals at high-risk of certain cancers is recommended.[109][125] Carriers of these mutations may then undergo enhanced surveillance, chemoprevention, or preventative surgery to reduce their subsequent risk.[125]
Management
Main articles: Management of cancer and oncology
Many treatment options for cancer exist, with the primary ones including surgery, chemotherapy, radiation therapy, hormonal therapy, targeted therapy and palliative care. Which treatments are used depends on the type, location, and grade of the cancer as well as the person's health and wishes. The treatment intent may be curative or not curative.
Chemotherapy
Chemotherapy is the treatment of cancer with one or more cytotoxic anti-neoplastic drugs (chemotherapeutic agents) as part of a standardized regimen. The term encompasses any of a large variety of different anticancer drugs, which are divided into broad categories such as alkylating agents and antimetabolites.[126] Traditional chemotherapeutic agents act by killing cells that divide rapidly, one of the main properties of most cancer cells.
Targeted therapy is a form of chemotherapy that targets specific molecular differences between cancer and normal cells. The first targeted therapies to be developed blocked theestrogen receptor molecule, inhibiting the growth of breast cancer. Another common example is the class of Bcr-Abl inhibitors, which are used to treat chronic myelogenous leukemia (CML).[127] Currently, there are targeted therapies for breast cancer, multiple myeloma, lymphoma, prostate cancer, melanoma and other cancers.[128]
The efficacy of chemotherapy depends on the type of cancer and the stage. In combination with surgery, chemotherapy has proven useful in a number of different cancer types including: breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer, and certain lung cancers.[129] The overall effectiveness ranges from being curative for some cancers, such as some leukemias,[130][131] to being ineffective, such as in some brain tumors,[132] to being needless in others, like most non-melanoma skin cancers.[133] The effectiveness of chemotherapy is often limited by toxicity to other tissues in the body. Even when it is impossible for chemotherapy to provide a permanent cure, chemotherapy may be useful to reduce symptoms like pain or to reduce the size of an inoperable tumor in the hope that surgery will be possible in the future.
Radiation
Radiation therapy involves the use of ionizing radiation in an attempt to either cure or improve the symptoms of cancer. It works by damaging the DNA of cancerous tissue leading to cellular death. To spare normal tissues (such as skin or organs, which radiation must pass through to treat the tumor), shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding, healthy tissue. As with chemotherapy, different cancers respond differently to radiation therapy.[134][135][136]
Radiation therapy is used in about half of all cases and the radiation can be from either internal sources in the form of brachytherapy or external radiation sources. The radiation is most commonly low energy x-rays for treating skin cancers while higher energy x-ray beams are used in the treatment of cancers within the body.[137] Radiation is typically used in addition to surgery and or chemotherapy but for certain types of cancer, such as early head and neck cancer, may be used alone.[138] For painful bone metastasis, it has been found to be effective in about 70% of people.[138]
Surgery
Surgery is the primary method of treatment of most isolated solid cancers and may play a role in palliation and prolongation of survival. It is typically an important part of making the definitive diagnosis and staging the tumor as biopsies are usually required. In localized cancer surgery typically attempts to remove the entire mass along with, in certain cases, the lymph nodes in the area. For some types of cancer this is all that is needed to eliminate the cancer.[129]
Palliative care
Palliative care refers to treatment that attempts to make the person feel better and may or may not be combined with an attempt to treat the cancer. Palliative care includes action to reduce the physical, emotional, spiritual, and psycho-social distress experienced by people with cancer. Unlike treatment that is aimed at directly killing cancer cells, the primary goal of palliative care is to improve the person's quality of life.
People at all stages of cancer treatment should have some kind of palliative care to provide comfort. In some cases, medical specialty professional organizations recommend that people and physicians respond to cancer only with palliative care and not with cure-directed therapy.[139] This includes:[140]
- people with low performance status, corresponding with limited ability to care for themselves[139]
- people who received no benefit from prior evidence-based treatments[139]
- people who are not eligible to participate in any appropriate clinical trial[139]
- people for whom the physician sees no strong evidence that treatment would be effective[139]
Palliative care is often confused with hospice and therefore only involved when people approach end of life. Like hospice care, palliative care attempts to help the person cope with the immediate needs and to increase the person's comfort. Unlike hospice care, palliative care does not require people to stop treatment aimed at prolonging their lives or curing the cancer.
Multiple national medical guidelines recommend early palliative care for people whose cancer has produced distressing symptoms (pain, shortness of breath, fatigue, nausea) or who need help coping with their illness. In people who have metastatic disease when first diagnosed, oncologists should consider a palliative care consult immediately. Additionally, an oncologist should consider a palliative care consult in any person they feel has less than 12 months of life even if continuing aggressive treatment.[141][142][143]
Immunotherapy
Main article: Cancer immunotherapy
A variety of therapies using immunotherapy, stimulating or helping the immune system to fight cancer, have come into use since 1997, and this continues to be an area of very active research.[144]
Alternative medicine
Complementary and alternative cancer treatments are a diverse group of health care systems, practices, and products that are not part of conventional medicine.[145]"Complementary medicine" refers to methods and substances used along with conventional medicine, while "alternative medicine" refers to compounds used instead of conventional medicine.[146] Most complementary and alternative medicines for cancer have not been rigorously studied or tested. Some alternative treatments have been investigated and shown to be ineffective but still continue to be marketed and promoted. Cancer researcher Andrew J. Vickers has stated: "The label 'unproven' is inappropriate for such therapies; it is time to assert that many alternative cancer therapies have been 'disproven'."[147]
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