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A new review found that certain cancers associated with people over 50 now affect people at younger ages more frequently. And obesity may be to blame.
Of the 20 most common cancers in the United States, the study found that nine are occurring in young adults. Approximately one in four new thyroid cancers were diagnosed in people aged 20 to 44, and about one in 10 new breast cancer cases occurred in that same age group, the researchers reported.
"Scientists have known for some time that obesity increases cancer risk, and when obese people get cancer, they're more likely to have a worse prognosis. And now it appears that obesity accelerates the development of cancer," said study author Dr. Nathan Berger. He is director of the Case Western Reserve University Center for Science, Health and Society, in Cleveland.
The researchers can't prove cause and effect. Still, the findings highlight the critical need for obesity prevention. "There are probably 140,000 cases of obesity-related cancers a year. This is a big issue," Berger said.
Experts generally agree that 13 cancers have clear ties to obesity. The current study found that nine of these 13 cancers are increasing in younger people. The nine cancers, and the percentage of new cases in people from 20 to 44, include:
- Breast cancer -- 10.5 percent,
- Colon and rectal cancer -- 5.8 percent,
- Kidney cancer -- 7.8 percent,
- Endometrial cancer -- 7.3 percent,
- Thyroid cancer -- 23.9 percent,
- Liver cancer -- 2.5 percent,
- Gastric cardia (cancer at the top of the stomach) -- 6.2 percent,
- Meningioma (cancer in the lining of the brain and spinal cord) -- 16.8 percent,
- Ovarian cancer -- 10.6 percent.
Boston oncologist Dr. Jennifer Ligibel said this study is a "really interesting first look at the incidence of obesity and cancer risk in young adults, but there's still a lot of work to be done."
She said the review does a nice job of gathering available evidence. But there's "not a huge body of information yet because weight has increased pretty significantly in young people in a short time, and we don't know the ramifications of that yet," added Ligibel, who is with the Dana Farber Cancer Institute.
Ligibel also chairs the American Society of Clinical Oncology's obesity and energy balance subcommittee. She wasn't involved in the study.
She said it's not clear exactly how obesity might increase cancer risk. "But it's probably not just one factor," she noted.
"Obesity causes higher levels of inflammation. It also causes higher levels of insulin and other growth hormones. Obesity leads to higher levels of sex hormones. Also, there are related factors, including diet. There's a lot we need to learn," she said.
Berger added that epigenetics are likely involved, too. Epigenetics are changes that occur in gene activity without changing the DNA itself.
Those kinds of changes may be lasting, even if someone who was heavy as a child loses weight, Berger said.
And even though the risk might not go away completely, it's still important to try to lose weight, he said.
Ligibel agreed, citing studies that showed the risk of cancer was cut by half for people who've had weight-loss surgery.
The study looked at 100 publications worldwide, with data reaching back more than four decades.
The review also points to the need for physicians to keep cancer on their diagnostic radar, even for younger patients. "If you have an obese patient with blood in the stool, evaluate them for colon cancer, even at a younger age," Berger suggested.
The review was published March 23 in the journal Obesity.
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SOURCES: Nathan Berger, M.D., Hanna-Payne professor, experimental medicine and director, Center for Science, Health and Society, Case Western Reserve University, Cleveland, Ohio; Jennifer Ligibel, M.D., oncologist, Dana Farber Cancer Institute, associate professor, medicine, Harvard University, Boston, and chair, American Society of Clinical Oncology's Obesity and Energy Balance subcommittee; March 23, 2018, Obesity