Research into cancer has never been more extensive, but there is little consensus on what is driving the sharp increase in diagnoses among young adults. In 2022, around 16% of the 20 million people with cancer worldwide were under 50. Between 1990 and 2019, the incidence of cancer in under-50s rose by 79%, according to a 2023 study in the British Medical Journal. This short timeframe rules out genetic factors, says Tracey Woodruff of the University of California, San Francisco.
Many early-onset cancers occur in wealthier countries, notes Kathryn Bradbury of the University of Auckland. About two-thirds of cancers in under-50s affect women. The most common early-onset cancers in 2019 were colorectal, breast and skin cancer. Prostate cancer and nasopharyngeal cancer increased fastest, while breast, stomach and bowel cancers caused the highest death tolls.
In 2024, Cancer Research UK and other organisations launched the Prospect project to investigate the global rise in colorectal cancer in under-50s. Rates are rising fastest in England, New Zealand, Chile and Puerto Rico. Risk factors under investigation include poor diet, particularly high consumption of processed meat, which is classified as a Group 1 carcinogen. Processed meats contain nitrates and nitrites that can damage bowel cells, though evidence in humans is limited.
Ultra-processed foods (UPFs), which make up 50-60% of daily energy intake in some high-income countries, are also a concern. A US study found that men in the highest fifth for UPF consumption had a 29% greater risk of colorectal cancer. However, experts caution that UPFs are a broad category, and risk may be linked to specific ingredients such as aspartame, a low-calorie sweetener.
Other potential factors include 'forever chemicals' (PFAS), declining birth rates, and environmental exposures, though research is ongoing. The rise in early-onset cancer is puzzling because younger populations are mainly non-smokers, says Mary Beth Terry of Columbia University. The Prospect project will examine multiple risk factors to identify causes and inform prevention strategies.
