Screening for Early Detection
In this section, you will learn:
Research identifying how cancer arises and progresses has led to the development of screening tests that can be used for early detection of cancer and precancerous lesions.
There are four types of cancer for which screening tests have been used widely to screen large segments of the U.S. population who are generally healthy and at average risk for the cancer being screened for.
Every person has a unique risk for each type of cancer based on his or her genetic, molecular, and cellular makeup, and his or her lifetime exposures to cancer risk factors.
Some people are at increased risk for certain types of cancer and may need to take risk-reducing measures, including adhering to a personalized cancer screening program.
There are significant disparities in cancer screening rates among certain segments of the U.S. population.
We need to develop new strategies to ensure optimal implementation of cancer screening for all.
Research has shown that most cancers arise and progress because of the accumulation of genetic mutations that disrupt the orderly processes controlling the multiplication and life span of normal cells (see Understanding Cancer Development). There are numerous factors that cause cells to acquire genetic mutations, including exposure to toxicants in tobacco smoke and UV light (see sidebar on Sources of Genetic Mutations and Figure 3).
Knowledge of the causes, timing, sequence, and frequency of the genetic, molecular, and cellular changes that drive cancer initiation and development provides opportunities to develop screening tests that can find, if present, precancerous lesions or cancer at an early stage of development (see Figure 7). If precancerous lesions are detected, they can be removed before they become cancer, something that is 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 a patient treated successfully.
What Is Cancer Screening and How Is It Done?
Cancer screening means checking for precancerous lesions or cancer in people who have no signs or symptoms of the cancer for which they are being checked but who are at risk for the disease (see Consensus on Using Cancer Screening Tests). People who have signs or symptoms suggesting the possible presence of cancer should see their health care providers promptly (see sidebar on Signs and Symptoms of Cancer).
There are four types of cancer for which screening tests have been developed and used to screen large segments of the U.S. population who are generally healthy and at average risk for the cancer being screened for (see sidebar on Cancers for Which Screening of Average-risk Individuals Has Been or Is Recommended).
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Consensus on Using Cancer Screening Tests
Screening for cancer has many benefits, but it also has potential risks (see sidebar on Cancer Screening). This is why cancer screening is not recommended for everyone. Determining whether and for whom a cancer screening test can decrease deaths from the screened cancer and provide benefits that outweigh the potential risks requires extensive research and careful analysis of the data generated.
In the United States, an independent group of experts convened by the Agency for 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 use of these tests. These volunteer experts form the U.S. Preventive Services Task Force (USPSTF). The evidence-based USPSTF recommendations fall into several categories, most prominently recommendations for screening certain individuals at certain intervals, recommendations against screening, and deciding that there is insufficient evidence to make a recommendation.
In addition to considering evidence regarding potential new screening programs, the USPSTF re-evaluates existing recommendations as new research becomes available and can revise the recommendations if necessary. For example, the USPSTF revised its recommendations for prostate cancer screening in 2018 (105). The revision was from recommending against screening to recommending that men ages 55–69 talk to a health care provider about the benefits and potential harms of screening before deciding if it is right for them.
Many professional societies also convene panels of experts to 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 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. For example, in 2018, the American Cancer Society began recommending that average-risk individuals start screening for colorectal cancer at age 45, rather than waiting until age 50 as the USPSTF and other professional societies recommend (106).
The existence of different cancer screening recommendations can make it challenging for individuals at average risk of those cancers to ascertain for which cancers to be screened and when. Nevertheless, there is more consensus than disagreement among recommendations about the use of the screening tests for the four types of cancer for which screening of generally healthy, average-risk individuals in large segments of the U.S. population has been or is recommended (see sidebar on Consensus Among Cancer Screening Recommendations for Average-risk Individuals). 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.
For individuals at average risk of developing a cancer for which there is a screening test, age and gender are the two main characteristics used to identify those for whom screening is recommended (see sidebar on Consensus among Cancer Screening Recommendations). However, each average-risk person is unique in his or her genetic, molecular, cellular, and tissue makeup (see sidebar on Breast Density), lifetime exposures to cancer risk factors, general health, and tolerance of the potential risks of a screening test. 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 situation.
A person’s situation can change over the course of his or her lifetime; for example, a woman whose screening mammogram leads to a breast biopsy that reveals certain noncancerous breast conditions, such lobular carcinoma in situ, is now at increased risk for breast cancer. Therefore, it is important that individuals keep up a dialog with their health care practitioners and continually evaluate their cancer screening plans, updating them if necessary.
Some individuals are at increased risk of certain cancers because they inherited a cancer-predisposing genetic mutation (see Table 3). If a person 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 his or her health care practitioner and consider genetic testing (see sidebar on How Do I Know If I Am at High Risk for Developing an Inherited Cancer?). Given that researchers are constantly learning more about the genetic causes of cancer, the number of mutations linked to cancer risk increases over time (25). Thus, it is important that individuals at high risk for inheriting a cancer-predisposing genetic mutation keep up a dialog with their health care practitioners and continually evaluate whether genetic testing is available and/or right for them. 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. As a result of the complexities of these tests, the FDA and Federal Trade Commission recommend involving a health care professional in any decision to use such testing, as well as to interpret the results.
If a person is at increased risk for developing a certain type or types of cancer, he or she should consult with his or her health care practitioner to 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 quitting smoking. 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 at average risk for the cancer (see sidebar on Examples of Cancer Screening for Increased-risk Individuals). Yet others may consider taking a preventive medicine or having risk-reducing surgery (see Table 5 and Supplemental Table 1).
As we increase our understanding of the genetic, molecular, and cellular characteristics of precancerous lesions, the inherited genetic mutations that increase a person’s risk for certain types of cancer, and the biology of cancer, we will be able to identify new biomarkers and develop new screening tests for more types of cancer (25)(109-110). We will also be able to better tailor cancer prevention and early detection to the individual patient, ushering in a new era of precision cancer prevention (111-112).
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Cancer Screening Tests Are Being Used Suboptimally
Even though the benefits of screening defined groups of individuals at average risk for breast, cervical, and colorectal cancer outweigh the potential risks (see sidebar on Consensus among Cancer Screening Recommendations for Average-risk Individuals), many individuals for whom screening is recommended do not get screened (see sidebar on Suboptimal Use of Cancer Screening Tests). In addition, a recent study found that just 2 percent of adults for whom lung cancer screening is recommended because they are at high risk for developing the disease had undergone screening in 2016 (113). Individuals who are not up to date with screening recommendations are disproportionately found in certain groups (see sidebar on Disparities in Cancer Screening) (114).
The suboptimal use of cancer screening tests and the significant disparities in cancer screening rates among certain segments of the U.S. population highlight the need for new strategies and public policies to increase cancer screening access and uptake. Identifying strategies to achieve this goal is an area of intensive research investigation. For example, one recent study showed that actively reaching out to adults not up to date with colorectal cancer screening by mailing them information about colorectal cancer risk and either sending them a stool test or following up by phone to schedule a colonoscopy increased screening uptake (116). Another study found that colorectal cancer screening rates were increased when patients attending a primary care appointment were provided access to an in-office app educating them about colorectal screening and allowing them to order their preferred test (117). Yet another study showed that a religiously tailored, mosque-based education program increased receipt of mammograms among Muslim American women (118).
Education is a vital part of all efforts to ensure optimal implementation of cancer screening. Clearly there is a lot more to do in this regard because a recent study found that just 20 percent of adults knew that the potential risks of cancer screening tests sometimes outweigh the beneﬁts (107). Increasing awareness of this fact among adults above the recommended age cutoff for a given cancer screening test and those with life-limiting medical conditions is particularly important because a substantial proportion of adults in these categories continue screening even though the evidence indicates that the benefits of screening are unlikely to outweigh the potential harms for them (119-121). One study found that the way in which health care practitioners put forward information can heavily influence whether older adults continue screening (119).
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