Rising bowel and ovarian cancer rates in younger adults raise new concerns

Cases of several cancers are rising in England among both younger and older adults, but rates of bowel and ovarian cancer are rising only among younger adults (under 50s), finds research published in the open access journal BMJ Oncology. 

Some other types of cancer are also rising faster in younger adults than they are in older adults, the findings indicate.  

While excess weight is a key contributor, it's unlikely to fully explain these patterns, say the researchers. 

The rising incidence of several cancers among the under 50s isn't unique to England, but it's not clear if changes in behavioral risk factors might explain these trends, highlight the researchers. 

To find out, they analyzed cancer incidence trends in England from the National Disease Registry Service for the period 2001 to 2019, comparing patterns by sex in two age groups: 20–49 year olds and those aged 50+ for more than 20 different cancer types.  

They used national health surveys to look at trends in established risk factors: smoking; alcohol intake; diet (high red/processed meat, low fibre intake); excess weight (BMI); and physical inactivity to quantify any changes by age and sex and estimate the proportion of cancers attributable to specific risk factors. 

Analysis of the data showed that new cases of 16 out of 22 cancers in younger women, and 11 out of 21 cancers in younger men, increased significantly in England between 2001 and 2019. 

In particular, there was a significant rise in 11 cancers with known behavioural risk factors among the under 50s. These were: thyroid; multiple myeloma; liver; kidney; gallbladder; bowel; pancreatic; womb lining (endometrial); mouth; breast; and ovarian cancers. 

Rates of all these cancers also rose significantly among the over 50s, with the notable exceptions of bowel and ovarian cancers.  

And 5 cancers-endometrial, kidney, pancreatic, multiple myeloma and thyroid cancer- increased significantly faster in younger than in older women, while multiple myeloma increased faster in younger than in older men. 

With the exception of mouth cancer, all 11 cancers were associated with obesity. And 6 (liver, bowel, mouth, pancreas, kidney, and ovary) were also linked to smoking; 4 (liver, bowel, mouth, and breast) were associated with alcohol intake; 3 (bowel, breast, and endometrial) were linked to physical inactivity; and 1 (bowel) was associated with dietary factors. 

But with the exception of excess weight, trends in these risk factors over the past one to two decades have been stable or improving for younger adults, with the largest reductions of around 7% in red meat consumption. 

The average daily amount of red meat eaten fell from 38 g in 2008 to 17 g in 2018 among younger men, and from 22 g to 10 g in younger women. And average processed meat intake in younger women was half that of younger men: 10 g vs around 20 g..

And while more than 90% of younger adults weren't eating enough fibre in 2018, their intake remained stable or slightly improved in both sexes between 2009 and 2019. And these trends were similar in older adults. 

Established behavioral risk factors accounted for a substantial share of cancer cases. In 2019 these contributed 68%–65% of mouth cancers for younger and older men, respectively; 42%–48% of liver cancers; 49%–53% of bowel cancers, 29%–33% of kidney cancers and 36%–34% of pancreatic cancers.  

Among women they accounted for 52%–45% of mouth cancers; 35%–42% of endometrial cancers; 44%–46% of liver cancers; 38%–42% of bowel cancers; 33%–37% of kidney cancers; 31%–28% of pancreatic cancers; and 19% to 24% of gallbladder cancers. 

Excess weight was the risk factor associated with most cancers in 2019, ranging from 5% for ovarian cancer to 37% for endometrial cancers. 

"These patterns suggest that while similar risk factors across ages are likely, some cancers may have age-specific exposures, susceptibilities, or differences in screening and detection practices," write the researchers. 

This is an observational data analysis, and as such, can't establish cause and effect. And the researchers acknowledge that there were no consistent, long term national data for several risk factors, and that their analysis was restricted to England rather than the UK. 

The findings were also based on the assumption of a 10-year lag period between exposure and cancer incidence. 

"The observed increasing cancer incidence despite declining trends in several behavioral risk factors may reflect the net effect of multiple influences operating in different directions. Other contributing factors not evaluated here, for example, reproductive history, early-life or prenatal risk factors, and changes in cancer diagnosis and detection practices, may also play a role," they explain.

 "Although overweight and obesity are linked to 10 of the 11 cancers evaluated and account for a substantial proportion of cancer cases, both BMI-attributable and BMI-non-attributable incidence rates have increased-though the latter more slowly-suggesting other contributors," they add. 

Several other risk factors have been mooted as driving the rising incidence of cases among younger adults, including ultra-processed foods, childhood obesity, physical inactivity/sedentary behavior, antibiotic use, sweetened drinks and air pollution. 

"While these factors are common in England, most have shown stable or declining trends in the last decade," although another suggested contributory factor-a disordered gut microbiome–merits further investigation, they point out. 

A degree of perspective is also needed, they suggest. "Although increases in cancer in younger adults are concerning, the absolute burden remains far higher in older adults, underscoring the public health and clinical importance of studying risk factors across all ages," they conclude.