Why are so many young people getting cancer? What researchers do and don’t know

A woman receives chemotherapy.Credit: Ricky Carioti/The Washington Post/Getty

Researchers around the world are grappling with a vexing problem: why are so many young people developing cancers once considered the purview of old age?

This question was prominent at two of the world’s largest cancer meetings this year, and hypotheses abounded. Ultra-processed foods, obesity, microbial toxins and agricultural chemicals were all considered. But a clear answer remained elusive.

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“Multiple cancers are increasing in incidence globally among individuals under the age of 50,” oncologist Kimmie Ng told the audience at the American Society of Clinical Oncology meeting in Chicago, Illinois, last week. “The vast majority are considered sporadic, with unknown cause.”

Worldwide, more than 9,000 cases of cancer are diagnosed each day in adults under the age of 50, epidemiologist Hyuna Sung told the annual meeting of the American Association for Cancer Research (AACR) in San Diego, California, in April. But lumping these diagnoses together could obscure clues as to their cause, she cautioned. “Rising incidence of cancers among young adults does not reflect a single story,” said Sung, who works at the American Cancer Society in Atlanta, Georgia.

Disparate causes

Clues to each story lie in the data. If diagnoses of a particular cancer increase suddenly and across all age groups, for example, the root cause might be a change in how that cancer is detected or classified. In the early 2010s, for example, the definition of pancreatic cancer was expanded to include pancreatic neuroendocrine tumours, which form in the pancreas’s insulin-making regions. Pancreatic cancer diagnoses had been rising slowly in the years before that change, but after it, the increase accelerated, including in people under the age of 50.

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The classification change probably does not explain the rise in early-onset pancreatic cancer fully, says Sung, but is likely to account for much of it.

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