Is Early-Onset Cancer a Global Epidemic?

Early-onset adult cancers—generally defined as cancers diagnosed in adults younger than 50— are increasingly becoming a global epidemic, according to an article published on 6 October 2022 in Nature Reviews Clinical Oncology.

This issue first attracted attention in colorectal cancer. Early-onset colorectal cancer has become more common. While this increase is well documented, the trend appears to extend far beyond colorectal cancer. Researchers tracked patterns of early-onset diagnoses over the past 30 years in 14 different cancer types, including breast, prostate and thyroid cancer, and found increases in many countries.

The authors reported that 8 of the 14 cancers studied were related to the digestive system. This highlighted the potential role of diet and suggested that the oral and gut microbiome may play a role in cancer risk. Many factors affecting cancer risk are modifiable, including diet, obesity, exercise, sleep and vaccination against HPV and other cancer-causing microorganisms.

Tomotaka Ugai and Shuji Ogino of the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, stated: "Our immediate goals should be to raise awareness of the early-onset cancer epidemic and reduce exposure to these risk factors."

The article reported that increased cancer screening contributes to earlier detection, but that some early-onset cancers also show a genuine increase in incidence.

In this study, Ugai, Ogino and colleagues reviewed the literature to map incidence trends for 14 cancer types among adults aged 20 to 49 in 44 countries between 2002 and 2012.

The researchers found that, since the 1990s, the incidence of early-onset cancers of the breast, colorectum, endometrium (uterus), oesophagus, extrahepatic bile duct, gallbladder, head and neck, kidney, liver, blood, pancreas, prostate, stomach and thyroid has increased worldwide.

For example, in the United States between 2002-2012, the average annual percentage change in kidney cancer incidence was 3.6% in women and 4.1% in men. For multiple myeloma, it was 2% in women and 3% in men.

The researchers acknowledged that "the specific effects of individual exposures are largely unknown". Nevertheless, the overall trend may reflect increased exposure to risk factors during early life and young adulthood.

Since the mid-20th century, major changes have occurred in diet, sleep, smoking, obesity, type 2 diabetes and environmental exposures. The researchers suggest that all of these may influence the gut microbiome or interact with our genes to increase early-onset cancer incidence. For example, obesity, smoking and alcohol are established risk factors for pancreatic cancer and are also associated with early-onset disease.

In conclusion, cancer is a multifactorial disease. We recognise the importance of genetics as a risk factor and screening for early detection, but this article highlights modifiable lifestyle habits that could substantially slow the rise of early-onset cancers. Although changes to factors such as diet and exercise could reduce their burden, implementing these changes is often difficult. More research is also needed to understand the roles of alcohol, obesity, physical activity and having children later in life. However, there is already sufficient reason to address these risk factors for both individual and public health benefits.