Cancer Progress Report 2016: Contents
In this section you will learn:
Understanding of the biology of cancer initiation and development has led to screening tests that can be used for cancer prevention and early detection.
There are five types of cancer for which screening tests have been developed and used in the clinic to screen generally healthy individuals.
Independent groups of experts rigorously evaluate data on the benefits and potential risks of cancer screening tests before putting forth recommendations about the use of the test; these recommendations are updated periodically to incorporate new evidence.
Areas of disagreement among different recommendations highlight areas in which more research is needed.
Some people are at increased risks for certain types of cancer and may need to take measures to reduce the risks.
The primary cause of cancer initiation and development is the accumulation of genetic mutations that disrupt the orderly processes controlling the multiplication and life span of normal cells. There are numerous factors that cause genetic mutation acquisition (see
Figure 3), and the identity, order, and speed at which a cell acquires genetic mutations determine whether a given cancer will develop and, if a cancer does develop, the length of time it takes to happen.
Knowledge of the causes, timing, sequence, and frequency of the genetic, molecular, and cellular changes that drive cancer initiation and development provides us with opportunities to develop screening strategies that allow us to detect, if present, precancerous lesions or cancer at an early stage of development (see
Figure 8). Precancerous lesions can be removed before they develop into cancer, something that is sometimes referred to as cancer interception. Finding cancer early, before it has spread to other parts of the body, makes it more likely that a cancer can be intercepted and the patient treated successfully.
There are five types of cancer for which screening tests have been developed and used in the clinic to screen generally healthy individuals (see sidebar on
Cancers for Which Screening Tests Exist). Some of these tests can be used to prevent cancer from developing
because they detect precancerous changes in a tissue that can be removed before they have a chance to develop into cancer. Others can detect cancer at an early stage of development, when it is more likely that a patient can be treated successfully. Recommendations on how best to use these tests are discussed in the information to follow.
One area of intensive research investigation aims to gain a deeper understanding of the biology of precancerous lesions (93, 94). The goal is that as we learn more about the genetic, molecular, and cellular characteristics of precancerous lesions, we can develop new screening tests and cancer prevention therapeutics, as well as more precisely identify those for whom cancer screening and cancer prevention therapeutics would be beneficial.
Who Should Be Screened?
Screening to detect cancer before an individual shows signs or symptoms of the disease for which he or she is being screened has many benefits, but it can also result in unintended adverse consequences (see sidebar on
Cancer Screening). Thus, population-level use of a cancer screening test must not only decrease deaths from the screened cancer, but it must also provide benefits that outweigh the potential risks. Determining whether broad implementation of a screening test across the population can achieve these two goals requires extensive research and careful analysis of the data generated.
In the United States, an independent group of experts convened by the Agency Healthcare Research and Quality of the US Department of Health and Human Services rigorously evaluates data regarding the benefits and potential risks of cancer screening tests to make evidence-based recommendations about the routine use of these tests. These volunteer experts form the U.S. Preventive Services Task Force (USPSTF). In addition to considering evidence regarding potential new screening programs, the USPSTF re-evaluates existing recommendations as new research becomes available and can revise them if deemed necessary.
Many professional societies also convene panels of experts to meticulously evaluate data regarding the benefits and potential risks of cancer screening tests, and each society makes its own evidence-based recommendations about the use of these tests. Because the representatives on each panel weighing the benefits and potential risks of a given cancer screening test are often different, and different groups give more weighting to certain benefits and potential risks than other groups do, this can result in differences in recommendations from distinct groups of experts.
The existence of different cancer screening recommendations can make it challenging for individuals to ascertain when and for which cancers they should be screened. Nevertheless, there is more consensus among recommendations than disagreement (see sidebar on
Consensus Among Cancer Screening Recommendations Screening Recommendations). The differences among the recommendations of different groups of experts highlight the areas in which more research is needed to determine more clearly the relative benefits and potential risks of screening, to develop new screening tests that have clearer benefits and/or lower potential risks, or to better identify people for whom the benefits of screening outweigh the potential risks.
Evidence-based cancer screening recommendations are only one consideration when a person makes decisions about which cancers he or she should be screened for and when. A consideration for some people is whether a screening test is covered by his or her health insurance. The enactment of the Patient Protection and Affordable Care Act of 2010, also known as “Obamacare,” increased the number of people covered by health insurance. It also includes a provision that requires qualified health insurance plans offered through health insurance exchanges, health insurance plans not designated as grandfathered, and Medicare to cover the costs of cancer screening tests recommended as grade A or B by the USPSTF. Individuals should check their own plans to see if they are covered. A consequence of this legislation is broader access to recommended screening tests for more people. For example, one recent study estimates that the enactment of this legislation enabled 6.8 million low-income women to gain access to health insurance, which should lead to increases in levels of cancer screening among this population (95). Further research is needed to confirm this result.
A person’s own unique risks for developing each type of cancer, his or her tolerance of the potential risks of a screening test, and his or her general health are also important considerations when deciding when and for which cancers to be screened (see sidebar on
Cancer Screening). A person’s overall risks are determined by genetic, molecular, cellular, and tissue makeup, as well as by lifetime exposures to cancer risk factors (see
Figure 3). Therefore, every individual should consult with his or her health care practitioner to develop a cancer prevention and early detection plan tailored to his or her personal cancer risks and tolerance of potential screening risks, as Congressman Donald Payne did (see p. 44). Given that these factors can vary over a person’s lifetime, it is important that individuals continually evaluate their cancer screening plans and update them if necessary.
Some individuals are at increased risk of certain cancers because they inherited a cancer-predisposing genetic mutation (see
Table 5) (96). If an individual has a family or personal history of cancer and thinks that he or she is at high risk for inheriting such a mutation, he or she should consult a physician and consider genetic testing (see sidebar on
How Do I Know If I Am at High Risk for Developing an Inherited Cancer). There are genetic tests that individuals can use without a prescription from a physician, but there are many factors to weigh when considering whether to use one of these direct- to-consumer tests (see sidebar on Direct-to-Consumer Genetic Testing).
In addition to cancer-predisposing genetic mutations, a number of medical conditions increase a person’s risk for certain types of cancer. For example, ulcerative colitis and Crohn disease increase an individual’s risk for colorectal cancer, and a complication of gastroesophageal reflux disease (Barrett esophagus) increases risk for esophageal adenocarcinoma (97, 98). These are all relatively rare conditions, but much more prevalent medical conditions also increase risks for certain cancers. For example, type 2 diabetes, which affects 9.5 percent of U.S. adults age 18 or over (20), increases an individual’s risk of developing liver, pancreatic, and endometrial cancers (99, 100).
If a person is at increased risk for developing a certain type or types of cancer, he or she can tailor risk-reducing measures to his or her personal needs. Some people may be able to reduce their risk by modifying their behaviors, for example, by smoking cessation. Others might need to increase their use of certain cancer screening tests or use cancer screening tests that are not recommended for people who are generally healthy; for example, the American College of Gastroenterology (although not the USPSTF) recently put forth recommendations about using endoscopy to screen people diagnosed with Barrett esophagus for precancerous lesions, esophageal lesions, and/or esophageal cancer (101). Yet others may consider taking a preventive medicine or having risk-reducing surgery (see Table 6 and Supplemental Table 1).
As we learn more about the genetic, molecular, and cellular characteristics of precancerous lesions, we will be able to develop and implement new strategies that pair this increased understanding with knowledge of an individual’s unique cancer risk profile, including his or her genetic makeup at birth, exposures to cancer risk factors, age, and gender. This information will allow us to better tailor cancer prevention and early detection to the individual patient, ushering in a new era of precision cancer prevention (26).
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Progress Report 2016 Contents