Rising Cancer Rates Among Younger Adults: Uncovering the Causes and Implications

The increasing number of breast, colorectal, and other cancers in people in their 20s, 30s, and 40s has become a concerning trend. Over the past decade, rates of colorectal cancer among individuals aged 25 to 49 have risen in 24 countries, including the UK, US, France, Australia, Canada, Norway, and Argentina.

At the UICC congress in Geneva in September 2024, an international team of researchers presented their preliminary findings. They surveyed data from 50 countries, revealing that in 14 of these countries, the rise in cancer cases was mainly observed in younger adults, while older adults' rates remained stable.

Breast cancer is one of the types of cancer where this trend is noticeable. A recent American Cancer Society (ACS) report found that although breast cancer death rates in women have dropped by 10% over the past decade, the incidence of breast cancer is rising by 1% per year overall, and by 1.4% per year in women under 50. The trend seems to have started in the 1990s, with one study showing a 79% increase in early-onset cancers from 1990 to 2019, and a 29% rise in cancer-related deaths in younger individuals.

This alarming trend has prompted major organizations like the UICC to focus on raising awareness among general practitioners, urging them to recognize early warning signs in younger patients. Sonali Johnson, head of advocacy at UICC, points out that doctors tend to take more serious notice of symptoms like fatigue and bloating in older adults, but may dismiss these symptoms in younger, seemingly healthy individuals, often attributing them to conditions like irritable bowel syndrome or stress.

Cancer specialists have noticed an increasing number of cases where younger patients develop cancers typically seen in older individuals. For instance, pancreatic cancer, usually diagnosed in people in their 70s, is increasingly affecting patients under 40. Dr. Eileen O'Reilly, a gastrointestinal oncologist, mentions that it’s now common to see pancreatic cancer in patients much younger than expected, with many being otherwise healthy and in their prime.

While oncologists have traditionally linked early-onset cancers to genetic factors, such as mutations in BRCA1 and BRCA2 genes, many younger patients show no clear genetic predisposition. In fact, the tumors in these younger patients tend to be more aggressive, leading to poor prognoses despite their good overall health.

There is an urgent need to understand the causes of this rising trend. Some researchers suggest that obesity and metabolic syndrome may be significant contributors, as they cause inflammation and disrupt hormonal pathways that increase cancer risk. A recent study found that accumulating excess body weight between the ages of 18 and 40 increases the risk of up to 18 different cancers. The Lancet study also noted that obesity-related cancers, such as those of the kidney, liver, pancreas, and ovaries, are on the rise among younger people in the US.

However, obesity alone does not explain the full picture. Many of the younger pancreatic cancer patients Dr. O'Reilly treats are fit and healthy, with no clear risk factors. This has led researchers to explore other factors, including the significant changes in sleep patterns worldwide over the past century. Dr. Shuji Ogino, a professor at Harvard University, believes that disrupted sleep and shift work may be contributing to this rise in early-onset cancers. Poor sleep quality has been linked to higher cancer risk, and exposure to artificial light at night—such as through streetlights and mobile devices—could be disrupting the body’s biological clock, further promoting cancer development.

The causes of the rise in early-onset cancers remain multifaceted, but as these trends continue, there is growing concern about the potential long-term impact on public health. The rising incidence of these cancers, combined with their often aggressive nature in younger individuals, presents significant challenges for both treatment and prevention.