Cancer screening, which often results in early detection, remains the most evidence-based method for improving cancer-related outcomes. Patients should be regularly evaluated for, and encouraged to participate in, recommended screening for early detection.

It is important to understand that cancer screening recommendations are dependent on individual risk factors. While some screening is recommended for all adults, regardless of risk level, high-risk individuals might be recommended to undergo earlier screening or screening for additional forms of cancer.

Dietary interventions, which involve adding and removing certain ingredients from the diet, are commonly promoted for cancer prevention. However, the research regarding dietary interventions is almost exclusively observational, and much of it has yielded mixed and conflicting findings.

The American Cancer Society recommends that people generally avoid drinking alcohol. For those that do choose to drink alcohol, the organization recommends no more than one drink per day for women and two drinks per day for men. These recommendations assume that one drink is equivalent to 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of hard liquor [10].

One of the largest analyses of this topic to date involved an "umbrella review," or a systematic review of prior systematic reviews and meta-analyses. This umbrella review incorporated only reviews and analyses of research conducted in humans, ultimately finding only weak, non-significant evidence of a link between the use of artificial sweeteners and cancer risk. The correlation remained weak and non-significant for cancer-related mortality as well [14].

Over the years, there has been a growing conversation about the potential for cruciferous vegetables to prevent cancer. The term "cruciferous vegetables" refers to vegetables that fall into the Brassica family, some of the more common of which includes broccoli, cauliflower, cabbage, kale, collard greens, radishes, and turnips.

A group of sulfur-containing chemicals called glucosinolates, which are found in these vegetables, have been the primary driver behind this cancer prevention push. When cruciferous vegetables are prepared, chewed, or broken down in the body, they break down into a number of individual compounds. Two of these compounds (indole-3-carbinol and sulforaphane) have shown anticancer effects in some animal studies. This anticancer activity seems to stem from a number of different mechanisms, including protection against DNA damage, inactivation of carcinogens, and induction of cell death in damaged cells [18].

Unfortunately, as with other dietary interventions, any evidence of benefit in cancer prevention is limited and observational in nature. To date, some smaller cohort studies in Europe and the United States have suggested that increased intake of cruciferous vegetables may be correlated with a modestly reduced risk of certain types of cancers, including colorectal and prostate. However, other cohort studies have not identified a link between cruciferous vegetable intake and cancer risk [18].

Antioxidants are an incredibly popular cancer prevention strategy. Supplements, foods, and drinks often tout their antioxidant content for this reason. Antioxidants are hypothesized to prevent the development of cancer by binding with cancer-causing free radicals in the body. Although in vitro and animal research has supported this theory, these findings have not carried over to clinical research. Prospective clinical research evaluating the benefits of antioxidant supplements in preventing cancer have been overwhelmingly negative [28].

Antioxidant vitamin supplements, including vitamins A, C, and E, have not shown benefit for preventing cancer overall, or for preventing prostate, lung, or gastric cancers, specifically. In fact, some studies even indicated a weak association towards an increased risk for cancer in some cases [28]. These findings, which showed a small increased risk of lung cancer in smokers, ultimately led to a USPSTF recommendation against the use of beta-carotene or vitamin E supplements for the prevention of cancer. The group also concluded that there was insufficient evidence to assess the balance of benefits and harms in using other vitamin and mineral supplements for the prevention of cancer [29].

While this link is not entirely understood, multiple mechanisms of action have been hypothesized. For example, increased physical activity can result in [37]:

Because obesity is also associated with many other serious health outcomes, such as diabetes and heart disease, all patients should be counseled on weight management. Modest weight loss of 5% to 10% in total body weight has been shown to result in measurable health benefits, including a reduced risk for chronic diseases. Although it is not clear how much weight loss is necessary to reduce a person's risk of cancer, weight loss (and particularly sustained weight loss) at a younger age is anticipated to reduce cancer risk. Research into this topic is currently ongoing, with a focus on people who have undergone bariatric surgery leading to maintained weight loss [41].

Tobacco use is the leading, established cause of cancer and cancer mortality. People who use tobacco products via any method (including smoking and chewing), as well as those who are exposed to tobacco smoke in their environments, are at an increased risk of cancer. Although most people associate smoking with lung cancer, it has actually been shown to increase the risk of many other forms of cancer as well, including cancer of the larynx, mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon, and cervix [44]. Use of tobacco snuff or chewing tobacco has been shown to increase the risk of mouth, esophagus, and pancreatic cancers [45].

Patients should be counseled to fully avoid the use of tobacco, in any form. Patients who are already using tobacco should be counseled on methods that may be helpful for quitting. There is currently no known safe amount of tobacco use via any method of administration [44]. Similarly, there is no safe amount of secondhand smoke from tobacco. Whenever possible, people should strive to spend their time in a smoke-free environment, and to provide a smoke-free environment to the people around them [46].