Unraveling cancer risk statistics
Almost daily, we’re bombarded by headlines about how personal habits, ranging from how much you drink to how often you work out, affect your cancer risk.
These numbers reflect important progress, signaling that scientists are unraveling some of the mysteries of cancer and providing health tips that could reduce your cancer risk. But health statistics can also seem murky and confusing, making it hard for people to know whether to change their behavior or just throw up their hands.
Consider the link between alcohol and cancer risk. Last March, Hutchinson Center researchers found that consuming 14 or more drinks per week boosts a woman’s breast cancer risk by 24 percent. More recently, a Hutchinson Center study found that drinking alcohol only elevates your risk of an uncommon type of breast cancer.
Within the scientific community, these findings reflect key steps in our understanding of cancer—steps that can be expanded and built upon as we work toward cures. But if you’re an everyday person trying to figure out how lead a healthy life, the numbers might leave you scratching your head.
Alcohol elevates breast cancer risk, and that’s true even if red wine is your drink of choice. But isn’t red wine supposed to be an elixir for heart disease and prostate cancer? How should I weigh the benefits and risks?
And if alcohol only increases the risk of an uncommon breast cancer, will cutting back really make a difference? What about other research showing that exercise reduces cancer risk? If someone likes to have two drinks a night, can they counteract the impact by exercising more?
To sort through these questions, I paid a visit to two of our breast cancer experts, Drs. Polly Newcomb and Julie Gralow.
Newcomb, who heads the Hutchinson Center’s Cancer Prevention Program, acknowledges that all the numbers paint “a confusing picture, especially for the general public who look at the science columns and get the impression that everything you do is associated with increased (cancer) risk.”
To cut through this, Newcomb uses her research to highlight relationships that are statistically significant—such as the relationship between breast cancer and wine. “People believe that red wine cancels out heart disease risk,” she said. “But when you look at the actual scientific literature on this, it’s only mildly compelling.” The link between alcohol and breast cancer, on the other hand, is relatively strong, Newcomb said.
Gralow is a practicing oncologist at the Seattle Cancer Care Alliance as well as a researcher, so she’s used to helping patients understand statistics. Her first piece of advice? Read “The Median Isn’t the Message” by the evolutionary biologist Stephen Jay Gould.
Gould wrote the essay after being diagnosed with abdominal mesothelioma, a rare cancer. Trained in statistics, he dove into the numbers and made a grim discovery. The median mortality rate for people in his condition was eight months, meaning that half of them died within that period. But Gould knew the data also meant that a small percentage of patients lived for years.
“I knew how to read data and not despair,” he wrote. So he focused on joining that group rather than assuming his days were numbered—and lived for 20 more years.
Gould’s overall point: statistics don’t account for the myriad possibilities and variations that biology and disease present. It’s a lesson Dr. Gralow emphasizes to many of her patients. “Statistics can be useful,” she told me, “but we have to remember they’re wrong for most people.”
That’s certainly true when it comes to alcohol and breast cancer. “For breast-cancer risk, a 24 percent increase looks whopping,” Dr. Gralow said, “until you remember that most people don’t get breast cancer.” Since only a small slice of the population contracts breast cancer, your chances of getting the disease are pretty slim, even after a 24 percent increase.
Gralow and Newcomb both said it’s wise to weigh your relative risks and focus on areas where you can make a significant difference. For example: given the strong link between obesity and cancer, and between exercise and reduced cancer risk, people can put a big dent in their risk by exercising and keeping their weight in check.
That doesn’t give you free license to hit the bottle. “It’s probably not good to use alcohol or have two drinks a night, if only because of the calories you’re consuming,” Dr. Gralow said. “But it’s probably not that bad to have a little wine each week, either.”
This underscores a larger point. As everyday people navigate their busy lives, they can’t be expected to know all their risk factors and which ones are larger than others. But a little common sense goes a long way.
That’s why Gralow advises people to follow a few simple rules—such as exercising regularly—and enjoy their lives. After all, Gralow regularly sees patients who had textbook healthy habits but still ended up with cancer. “You can reduce your risk,” she said, “but you can never eliminate it.”
By Justin Matlick
Quest science writer