By the year 2030, the number of people diagnosed annually with cancer worldwide could reach 21 million. This week, the Union for International Cancer Control (UICC) is meeting in Montreal to discuss how to diminish the rising tide of cancer.

The long-term solution, experts think, lies in another startling statistic: that 40% of cancers stem from factors that we can control.

At the meeting, the American Institute for Cancer Research and the World Cancer Research Fund International (AICR/WCRF) rolled out the latest update to the world’s largest central database of research on how lifestyle choices influence the risk of cancer. Key causes of “preventable” cancer include unhealthy diets, lack of exercise, being overweight, alcohol and tobacco, and not taking full advantage of preventive vaccinations and screenings.

“The fact is that changes in our lifestyle can powerfully protect us against cancer,” says Dr. Anthony Komaroff, editor in chief of the Harvard Health Letter and a professor of medicine at Harvard Medical School. “In fact, we can do more to protect ourselves against cancer than our doctors can do for us.”

Unfortunately, even the healthiest lifestyle won’t immunize you against cancer. “Age and genetics outweigh many of these risk factors,” says Dr. William Kormos, editor in chief of Harvard Men’s Health Watch and a primary care physician at Harvard-affiliated Massachusetts General Hospital.

For example, having a first-degree relative—a parent or sibling—with colon or prostate cancer could double your risk. At the same time, the healthier your choices, the more benefit you are likely to gain.

“What science needs to do now is figure out how these lifestyle factors influence the risk of cancer,” Dr. Komaroff says. “What are the changes in body chemistry caused by these lifestyle factors that influence the development of cancer? If we can figure that out, we might identify targets for new anti-cancer drugs.”

In all the hopeful discussion of lifestyle’s role in cancer, it is important to remember that millions of people are newly diagnosed every year. For them, the mere mention of “preventable cancer” can feel like an indictment.

“Someone who has unfortunately developed cancer, and who may have had an unhealthy lifestyle, can feel that they are being blamed,” Dr. Komaroff says. “It’s bad enough to learn you have cancer, particularly if it is of a kind that is likely to end your life prematurely. To add guilt on top of that is just adding to the suffering.”

But the lesson from Montreal is not about laying blame, but creating hope. Taking the best care of your body as you can is still the cheapest and one of the most effective ways to save the lives of people not yet in the grip of cancer.