If you're 20, here are 5 decisions you can make to avoid cancer over the next 20 years

It's wise to think ahead when it comes to cancer, says William Nelson, one of the nation's leading oncologists and director of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University.

That includes taking steps like avoiding tobacco and tanning beds, especially when you're young.

Nelson recently did a Q&A session on Quora, where he covered everything from why cancer is hard to solve and what role genomics should play in its treatment.

One question, though, offered some more concrete advice. Here's what the leading oncologist had to say to a 20-year-old who asked what decisions they could make over the next 20 years to avoid cancer:

• "The most important thing you can do, of course, is to avoid use of tobacco in any form. Lung cancer is the leading cause of cancer death in the U.S. for both men and women, and people who smoke are 25 times more likely to develop lung cancer than those who don't. Tobacco use is also associated with increased risk of 18 different cancers, including cancer of the larynx, bladder, cervix, stomach, and colon."
• "Leading an otherwise healthy lifestyle also reduces your cancer risk. That includes controlling your weight (be as lean as possible without becoming underweight); getting exercise (at least 30 minutes a day of physical activity), minimizing consumption of alcohol, and limiting consumption of foods high in fat or added sugars (because these contribute to weight gain), among others. It's believed that maintaining a healthy lifestyle reduces the incidence of cancer by 10 to 15 percent and mortality from cancer by 20 to 25 percent."
• "Other important precautions include avoiding excessive exposure to the sun, which can cause skin cancer, including melanoma, which can be fatal. And stay out of tanning beds! According to the American Academy of Dermatology, people who use indoor tanning are 59 percent more likely to develop melanoma than those who have never done it."
• "You should have an annual checkup with a physician and follow his or her recommendations for age-appropriate screening. You should also know your family history of cancer and share that with your physician. For example, a woman with a family history of breast cancer, especially certain kinds, has a higher risk of developing breast cancer herself. Regular screening is even more important in those cases."
• "Both men and women should also check with their doctors to make sure they have been vaccinated for the human papillomavirus (HPV), which causes cervical and other cancers, and hepatitis B (HBV), the cause of most liver cancers."