Century-old tumor samples may help explain rising rates of colorectal cancer in younger adults

Scientists are turning to tumor tissue samples up to 100 years old and stored in a London hospital to try to solve the mystery behind surging colorectal cancer rates among younger adults.

Though the overall rate of colorectal cancer has been declining, it has been rising among people 55 and under by 1% to 2% each year since the mid-1990s, with 1 in 5 people diagnosed with colorectal cancer now under 55. Colorectal cancer has become the leading cause of cancer death among men under 50 and second among women in the same age range, according to the American Cancer Society.

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The reason colorectal cancer rates have been rising among younger adults is still unclear. Increased consumption of ultra-processed food, more sedentary lifestyles and rising obesity rates may all be contributing factors, researchers says.

The basement archives at St Mark's The National Bowel Hospital in London contains tens of thousands of tumor tissue samples and gut bacteria – preserved in paraffin – from every patient ever treated there for colorectal cancer. This makes the hospital the most "unique resource probably anywhere in the world" for uncovering the reasons for the rising cancer rates, Dr. Kevin Monahan, a consulting gastroenterologist at St Mark's hospital, told the BBC.

The samples are now being sent to the Institute of Cancer Research in the United Kingdom for molecular DNA analysis to help learn how patterns of colorectal cancer in younger adults have shifted through the years, the BBC reported.

A particular type of gut bacteria, or E. coli, now present in people's bowels but not in the past, may be a culprit. The bacteria may be emitting toxins that lead to the growth of cancerous cells, said Trevor Graham of the Institute of Cancer Research.

Scientists are hoping this "treasure trove" of bowel tissue samples stored in the hospital will allow scientists to test this hypothesis and others, Graham said.