Obesity-related cancers rising in U.S. young adults

Millennials were nearly five times as likely as baby boomers to develop cancer of the kidneys

If the obesity epidemic continues, there could be an explosion of fat-sensitive cancers in the years to come. (designer491/Shutterstock)

Mirroring the decades-long increase in obesity rates in the U.S., cancers that are thought to be driven at least in part by excess weight are also on the rise among people under age 50, a new study suggests.

Rates for six of 12 cancers related to obesity have been increasing in successive generations of young adults, with the sharpest increases in the youngest age groups, researchers report in The Lancet Public Health.

The new study may serve as a warning that if the obesity epidemic continues, there could be an explosion of these fat-sensitive cancers in the years to come, said the study's senior author, Dr. Ahmedin Jemal, scientific vice president of surveillance and health services research at the American Cancer Society.

"This finding signals an increased burden of obesity-related cancers in older adults in the future and calls for actions to mitigate this burden," he said in an email.

The researchers analyzed data from a central database of state cancer registries, focusing on new diagnoses between 1995-2014 of 30 types of cancer, 12 of which are associated with excess weight. They had complete data from 25 states that represent about two thirds of the U.S. population.

In that 20-year period, there were about 14.7 million new cases of the 30 cancers. For at least eight cancers, including smoking-related and HIV-associated cancers, the incidence rates dropped.

But for six of the 12 obesity-related cancers — colorectal, endometrial, gallbladder, kidney, pancreas and multiple myeloma  there was a steady increase in incidence over the years, with larger increases in younger adults.

The annual rise in new cases of kidney cancer, for example, was 6.23 per cent among people aged 25-29, but about 3 per cent in the 45-49 age group. Similarly, pancreatic cancer incidence rose 4.3 per cent each year for 25-to-29-year-olds but less than 1 per cent annually among people aged 45-49.

Overall, rates of colorectal, endometrial, pancreatic and gallbladder cancers in millennials — young adults born around 1985 — were about double the rates seen in people born in the 1950s at the same age, the researchers note.

Especially striking was the rising rate of kidney cancers. Millennials were nearly five times as likely as baby boomers to develop cancer of the kidneys.

In contrast, for all but two of the 18 non-obesity related cancers, rates either stabilized or declined in successive younger birth cohorts.