The rate of cancers in young adults is rising, and scientists are working to find what is behind the increase, The New York Times reported Oct. 1.
A study published in May found that rates for 14 cancers have increased in people younger than 50. These early-onset cancers remain rare, but rates have been steadily rising since the 1990s. More screening and better detection can explain some of the rise of early-onset cancer diagnoses.
Researchers have been diving into what else could be behind the rising rates, and several recent studies have found that mutations alone are not a sufficient driver of cancers. Scientists are finding that lifestyle and environmental factors are playing a key role in mutations that create cancer-causing genes and tumors that take decades to develop.
Environmental, lifestyle factors
People born in or around the 1950s had higher rates of early-onset cancer in the 1990s. But those born in the 1990s have a two- to threefold increased risk of certain cancers compared to their earlier counterparts. This “birth-cohort effect” suggests exposures from the environment or lifestyle that has become more common in recent decades.
These factors include less physical activity, consuming more processed foods and sugar, exposure to more plastics and forever chemicals, and sleeping less. Any of these factors can play a role in early-onset cancers, though the link has not yet been strongly proved.
However, there is evidence to link cancer to obesity, alcohol use and poor diet. A review of nearly 15 million cancer cases in the U.S. found that incidence of six obesity-related cancers rose in young adults between 1995 and 2014, with steeper rises in younger generations. The western diet — characterized by high amounts of red and processed meats, sugary drinks and ultraprocessed foods — also was linked to early-onset colorectal cancer, researchers told the Times.
Biological factors
Women are disproportionately affected by early-onset cancers, partly because breast cancer is one of the most common forms of cancer. The increase in breast cancer rates could be linked to a widening gap between when girls get their periods and when they have their first pregnancy.
Girls in the U.S. are now getting their periods around age 11 or 12, slightly younger than previous generations, and on average have their first pregnancy at 27, up from their early 20s. This longer gap between first period and first pregnancy could be leaving breast tissue more exposed to cancer cells and mutations. During this interval, cells are particularly susceptible to radiation, alcohol and metabolic disruption. This can leave women vulnerable to harm for longer, and let DNA damages accumulated in their 20s develop over a lifetime.
However, during pregnancy and breastfeeding, research suggests that the number of immune cells increases in the breast, protecting it against potentially cancerous cells. When a baby weans, the immune system leaves fewer mutated cells behind and the remaining cells spend more time repairing DNA, researchers told the Times.
Early genome changes
Some links can be traced to as early as in the womb, where certain exposures may change genetic code and accelerate cancer development.
In the gut, cells switch between more and less developed stages. When these gut cells in young people are confronted with a stressor, they revert to a less developed stage. In older adults, these cells die off. But the less developed cells can behave aggressively and lead to cancer.
Some studies of cancer genomes have shown early-onset colorectal cancer patients having more mutations associated with a bacterial toxin called colibactin. This toxin can be produced by some strains of E. coli and other bacteria. These infections typically occur in the first two to three years of life and can put children who get infected at higher risk of developing cancer.
The gene for this toxin is found in up to 40% of children’s stool samples in industrialized nations and virtually absent in nonindustrialized nations, meaning it could be tied to factors such as food and antibiotics, experts told the Times.
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