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Many cancers are preventable. Cancer prevention focuses on modifying environmental and lifestyle risk factors that promote cancer. Smoking is the most well known of these behaviors, but other characteristics — such as body weight, physical activity levels, and alcohol intake — influence one’s risk of developing cancer as well. Obesity alone has been linked to 20% of cancer cases, and some estimate that the population-level burden of obesity may now exceed that of cigarette smoking.
Breast cancer can be used as an example to examine the ways in which these lifestyle behaviors can promote cancer development. Obesity is a documented risk factor for breast cancer. An elevated body mass index (BMI) is associated with higher rates of hormone receptor-positive tumors in postmenopausal women. This is thought to be due to increased estrogen production by fat tissue.
As might be expected, weight gains in this population (of 10 kg or more) were associated with an increased risk for breast cancer compared with those with stable weight (relative risk [RR] 1.18, 95% CI 1.03-1.35, P=0.002 for trend), while weight loss among those who never used postmenopausal hormones, lost at least 10 kg, and kept this weight off, was associated with a decreased cancer risk (RR 0.43, 95% CI 0.21-0.86, P=0.01 for trend).
The correlation between obesity and risk of breast cancer has not been demonstrated in premenopausal women. Still, attention to BMI is important in these patients as well. In women with BRCA mutations, weight loss has been shown to decrease the risk of developing breast cancer, demonstrating that even this well-known oncogene is partially modulated by BMI. There is no specific diet composition that is linked to breast cancer risk reduction. More important is a diet that allows one to maintain a healthy BMI, regardless of age.
Along these lines, increased physical activity levels are also associated with a decreased risk of breast cancer. Multiple studies, both prospective and retrospective, have demonstrated that higher levels of physical activity are protective against breast cancer development when compared with sedentary lifestyles. National Comprehensive Cancer Network (NCCN) guidelines recommend vigorous physical activity in premenopausal women, and at least moderate physical activity in postmenopausal women.
Alcohol use is another modifiable risk factor associated with the development of breast cancer. There has been much research regarding the potential benefits of moderate alcohol consumption in the general population. However, these same “moderate” levels of alcohol intake (1-2 drinks per day depending on gender) have been linked to increased risk of breast cancer. While there have not been studies evaluating reduction in alcohol intake and subsequent incidence of breast cancer, the NCCN continues to recommend that women limit alcohol intake to less than or equal to 1 drink per day.
It has been shown that individuals adhering to four healthy behaviors (never smoking, maintaining a BMI below 30, being active for more than 3.5 hours/week, and eating a healthy diet) have one-third the risk of developing cancer than individuals adhering to none of these behaviors. While smoking may not be the widespread issue it once was, obesity, physical inactivity, and unhealthy dietary intake are well on their way to becoming public health crises of their own. Reducing the risk of cancer development in any patient should include attention to modifying these behaviors.
Early Detection of Cancer
To say that we are on the right path with our approach to studying and treating cancer would be difficult to support. To the contrary, we may be in need of a dramatic shift in our tactics.
Drug development has been the objective of cancer research for decades. However, for all the effort this has required, and the associated costs (cancer care in the U.S. will cost $175 billion this year), one would hope to have seen more progress by this point. Instead, in an analysis of the more than 70 drugs approved for the treatment of cancer by the FDA from 2004 to 2014, the average prolongation in survival was 2.1 months. Moreover, some diseases still have the same standard of care they had 50 years ago. Acute myeloid leukemia has a 5-year survival rate of 24%, with bone marrow transplant increasing these odds to 50% in the best-case scenario. These figures have remained relatively the same since the 1970s.
In citing any progress that has been made against cancer overall, cancer prevention and early detection often do not receive their due credit. Public health efforts have led to decreases in smoking that have correlated directly with the decrease in overall cancer mortality. Cancer screening, through effective modalities such as colonoscopies and pap-smears, have saved countless lives as well. Cancer remains a formidable foe, but it may be time to shift our focus from trying to save patients in the end stages of their disease with expensive drugs to trying to catch cancer early with inventive screening and monitoring techniques. For eight common cancers combined, the 10-year survival rate for patients diagnosed at an early stage is 81%, more than three times greater than when diagnosed at advanced stages (26%).
Researchers are working toward innovation in the early detection arena. Sanjiv Gambhir, MD, PhD, and the Canary Center at Stanford for Cancer Early Detection in California, are working on ways to monitor the health of individuals with greater frequency, in order to detect the first signs of illness. For instance, the “smart toilet” would monitor the molecular contents of bodily fluids daily. Abnormalities, such as mutated DNA suggestive of colorectal cancer, would be marked for physician review. They are also developing a smart bra, designed to continuously image breast tissue. These inventions are a long way from clinical use, but it is encouraging to know that these sorts of novel tools may be on the horizon.
Other promising approaches to early detection are so-called “liquid biopsies.” A group at Johns Hopkins developed CancerSEEK, which measures a variety of cancer proteins and mutated DNA in the blood. This technology correctly detects the presence of cancer in 70% of patients with known malignancies, several of which (ovarian, liver, pancreas) have no currently approved screening tool.
Early detection is not a panacea. There are many issues with the current screening tests — overdiagnosis being the most important — and the above-proposed technologies might be prone to the same issues. However, toxic therapies (chemotherapy, radiation, surgery) have taken us only so far, and the highly expensive novel agents brought to market recently (immunotherapy, chimeric antigen receptor [CAR] T-cell therapy) have their own toxicities. The damage that these existing modalities can inflict, often in the name of only a few extra months of survival, fail to inspire. If we were able to shift our focus toward trying to find the first signs of cancer — harnessing the successes of cervical and colon cancer screening — we could make inroads against the malignancies that may never be cured by drugs alone.
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Last Updated May 07, 2020