Screening age needs to be lowered to combat colorectal cancer 'epidemic,' say researchers

New Zealand needs to lower the screening age for colorectal cancer if it wants to reverse the dramatic increase of people aged under 50 being diagnosed and dying from the disease, University of Otago researchers say.

In an editorial in this week's New Zealand Medical Journal, Dr. Oliver Waddell, Dr. Tamara Glyn and Professor Frank Frizelle say Aotearoa is part of a world trend in which the number of people aged under 50 being diagnosed with bowel cancer—referred to as early onset colorectal cancer—is increasing.

From 1995 to 2012, colon cancer in New Zealand men aged under 50 increased by 14%, and in women by 13%.

The figures are even more concerning for Māori who are disproportionally affected by early onset bowel cancer—30% of bowel cancers in females and 25% in men occur before the age of 50.

The trend is consistent with other studies from Australia, the United States, Canada, the United Kingdom, France and Asia, which all show a rapid increase in bowel cancer in those aged under 50. In the United States, the incidence of early onset bowel cancer has doubled since the 1990s and by 2030 it has been estimated that more than one in 10 colon cancers and nearly one in four rectal cancers will occur in people aged under 50.

Countries that start screening at age 40 seem to have avoided the impact of this shift, Dr. Waddell says.

New Zealand—where bowel cancer is the second biggest cancer killer—has one of the highest screening ages in the world. The National Bowel Screening Program is currently only open to people aged 60 to 74. Australia screens for bowel cancer from age 50 however it is available to those who request it from age 45.

"A review of international trends in early onset colorectal cancer incidence rates across five continents found only three countries where the incidence rates were decreasing. Two out of these three countries—Italy and Austria—have been screening patients from the age of 40 or 44 since the 1980s," Dr. Waddell says.

The American Cancer Society recommends that screening should begin at age 45 and their modeling shows that this would result in an additional 22 to 27 life years gained per 1,000 people screened.

"If the age of eligibility for screening in New Zealand were lowered to 40 or 45 it would be likely to result in a proportional decrease in the diagnosis of early onset colorectal cancer as seen in countries with a lower age of screening."

The incidence of early onset bowel cancer in New Zealand from 1995–2020 found that 45% were aged between 45 and 49.

"This means that almost half of those early onset cases may either be prevented or diagnosed earlier if screening was lowered to 45, and more so if reduced to 40," he says.

The cause for this rise is likely to be largely environmental factors and is likely to be involved with alterations in the bacteria living in the gut. A large variety of loosely associated factors have been suggested to contribute to the trend of younger bowel cancer patients, such as changing trends in obesity, sedentary lifestyles and smoking, but the cause has not yet been proven.

"Until the cause of this avalanche can be identified and addressed, we must act to mitigate the consequences. Lowering the screening age is the most effective tool we have to combat this epidemic.

"This simple action would improve equity and outcomes for all New Zealanders."