In 2020, a year of unimaginable tragedy, an estimated 375,000 people died from Covid-19 infections in the United States alone. Much of the suffering and death due to the disease was preventable in three ways: through avoidance by wearing masks and social distancing; by screening and treatment; and by vaccination.
One of the lessons of the Covid-19 pandemic has been that effective prevention strategies and widely used screening tests, combined with treatment and vaccines, can be developed and deployed rapidly across the country. We need to do the same thing for cancer prevention.
During the first pandemic year, more than 1.8 million Americans heard the frightening sentence, “You have cancer.” During the same period, nearly 600,000 Americans died from cancer, many more than the number who died from Covid-19 that year. But unlike the precipitous declines in Covid-19 cases and deaths, cancer will likely take a similar toll year after year.
In the 50 years since the passage of the National Cancer Act of 1971, we have learned that cancer prevention using those same strategies — avoidance, screening, and vaccination — along with intercepting precancerous changes averts more cancer deaths than cancer therapy does.
Prevention is the first and best line of defense for many cancers. When it works — and it does work — prevention generally goes unnoticed. In contrast, it is easy to build excitement around advances in treatment when new therapies yield benefits in patients. These are visible, helping people with cancer live longer, healthier lives. But when prevention works, there is nothing to show. Cancer simply does not occur. Healthy people stay healthy.
Proven opportunities to prevent cancer abound, yet the uptake of these readily available strategies has been imperfect.
Cancers can be prevented by avoiding things that cause them. Take tobacco as an example. Never using tobacco products, or stopping their use, has proven cancer-preventing effects. While fewer people smoke today than in years past, thanks to policy changes and education campaigns, approximately 1 in 14 adults and 1 in 8 high school students still use tobacco products. Avoiding weight gain by eating a healthy diet and exercising helps reduce cancer risk partly because obesity and type 2 diabetes (which is linked to weight) contribute to the development of several cancers.
Screening tests have been proven to reduce the number of cases and deaths for certain cancers. These include screening for colorectal cancer, for lung cancer among those who are or have been heavy smokers, and for breast and cervical cancer among women.
More than half of cervical cancers diagnosed in the U.S. occur in women who have not been tested for the disease, or tested only sporadically for it, and this type of cancer is found at later stages than in women who are routinely screened for it. Almost one-third of adults are not up to date on their colorectal cancer screening. Less than 10% of those eligible for lung cancer screening follow through with it. And while there is effective testing and treatment of hepatitis C, a major cause of liver cancer in the U.S., approximately half of those who have the virus that causes the disease do not know they have been infected with it.
Effective vaccines exist that prevent cancer-causing infections. Vaccination against human papillomavirus is highly effective at preventing HPV infection, which causes virtually all cervical and anal cancers, as well as many penile, vulvar, vaginal, and mouth and throat cancers. Yet more than 50% of adolescents ages 13 years to 17 years have not completed their HPV vaccination series. Hepatitis B is a major cause of liver cancer worldwide, and though vaccines against it have existed for more than 40 years, approximately 75% of Americans are not vaccinated against it.
Unlike Covid-19, preventive agents for cancer go beyond vaccines. A variety of non-vaccine agents can help prevent cancer, including daily, low-dose aspirin for some people at risk of colorectal cancer, and selective estrogen receptor modulators such as tamoxifen and raloxifene for women at elevated risk of breast cancer.
The future of cancer prevention research is promising. Scientists are identifying new ways to make it more accessible and convenient. People can already check for colorectal cancer with at-home kits. It will soon be possible to test for cervical and liver cancer at home. By making it easier for people to get checked for cancer, more people will do it.
Researchers also are evaluating new blood tests, sometimes called liquid biopsies or multi-cancer early detection tests, which can spot multiple cancers from one sample. And who knows what other interesting cancer prevention research ideas may emerge from the proposed Advanced Research Projects Agency for Health (ARPA-H), which is in the president’s FY2022 budget?
Physicians will increasingly “personalize” cancer prevention, just as they are doing in other areas of cancer care. The day is approaching when physicians will be able to use knowledge about individuals’ lifestyles, biology, and genetics to tailor cancer prevention approaches for them. Physicians can use this information, for example, to decide who needs to start cancer screening earlier and who can safely wait. The National Cancer Institute is working on identifying specific agents to intervene and modify precancerous changes in cells before they become cancerous. Vaccines that harness the immune system to attack these precancerous changes are on the horizon as well.
Prevention is the 21st century “cure” for cancer. While it is unlikely we will ever be able to prevent all cancers, many can be prevented now and many more can be prevented in the future. Ending cancer as we know it is the mission of the National Cancer Institute. What better way to achieve that goal than by preventing as many cancers as we can?
Philip E. Castle is the director of the National Cancer Institute’s Division of Cancer Prevention.
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