Obesity-related cancers increasing in young US adults

Breast Cancer

Rates of some obesity-related cancers rising faster in adults aged 25 to 49 than in older generations

An observational study using data covering more than half of the US population suggests that incidence rates of cancers linked to obesity are increasing most rapidly in young adults. The findings, published in The Lancet Public Health journal on World Cancer Day, could indicate that an even greater disease burden is on the horizon.

The study suggests that the sharpest increase in obesity-related cancer incidence is in adults aged 25 to 49. This was true for half of the 12 cancers classified as related to obesity: colorectal, uterine corpus, gallbladder, kidney, pancreatic, and multiple myeloma (a type of bone marrow cancer). Patients were divided into five-year age groups from 25-29 to 80-84 years old. Each successively younger age group experienced a greater percentage increase. Of the 18 other types of cancers included in the study only two showed a similar trend while eight – mostly related to smoking, infection, or both – showed a decline, and the rest remained stable.

Despite these increases in risk, the authors note that the overall incidence of these cancers remains higher in older age groups than in younger age groups

Despite these increases in risk, the authors note that the overall incidence of these cancers remains higher in older age groups than in younger age groups.

“Our findings expose a recent change that could serve as a warning of an increased burden of obesity-related cancers to come in older adults,” says Dr Ahmedin Jemal from the American Cancer Society, USA. “Most cancers occur in older adults, which means that as the young people in our study age, the burden of obesity-related cancer cases and deaths are likely to increase even more. On the eve of World Cancer Day, it’s timely to consider what can be done to avert the impending rise.”

Most epidemiological studies have focused on older populations so the effect on cancer risk of excess bodyweight in early life, or of weight gain in young adulthood, is not well understood. In some cancers, excess bodyweight during early adulthood could be a more important influence on cancer risk than weight gain in later life. This is the first study to examine contemporary incidence trends in young adults for a comprehensive list of cancers in the United States.

The researchers analysed incidence data from 25 state cancer registries, covering 67% of the US population. They considered 30 of the most common cancer types, including 12 obesity-related cancers in people aged 25 to 84 years, diagnosed between 1995 and 2014. During this timeframe, there were 14,672,409 cases of the 30 types of cancer.

Incidence of multiple myeloma and cancers of the colorectum, uterine corpus, gallbladder, kidney, pancreas, and thyroid increased in younger adults (25 to 49 years). Incidences also rose in older adults, except for colorectal cancer, but by a smaller percentage. The younger the age group, the greater the size of the increase – in all seven of the cancer types except for thyroid cancer. For example, in pancreatic cancer the average annual change was equal or less than 1% in people aged 40 to 84, 1.3% in those aged 35 to 39, and 2.5% in 30 to 34-year-olds. In the youngest age group (of 25 to 29 years), it was 4.3%. Across the six cancer types, the annual increase ranged from 0.4% in uterine corpus cancer to 3.0% in kidney cancer amongst 45 to 49-year-olds, and from 1.4% for multiple myeloma up to 6.2% in kidney cancer in 25 to 29 year-olds (see Figure 3 for trends in age-specific incidence rates for the 12 obesity-related cancers between 1995–2014).