Incidence of solid and haematological cancers has risen 79% among under-50s around the world over the past three decades, with the biggest increases in wealthy countries like Australia, research has found.

Breast cancer accounted for the highest number of ‘early onset’ cases in this age group in 2019, but nasopharyngeal and prostate cancers have risen the fastest since 1990, the analysis reveals.

Global multiple myeloma and non-Hodgkin lymphoma incidence both rose over the 30 years, although leukaemia and Hodgkin lymphoma rates fell slightly.

The findings upend received wisdom about the types of cancers typically affecting the under 50s, a linked editorial suggests.

The researchers noted that while older people remained in the overwhelming majority of cancer diagnoses and deaths, evidence had been building that cases have been rising in younger patients in many parts of the world.

But most of these studies have focused on regional and national differences; and few have looked at the issue from a global perspective or the risk factors for younger adults, write the researchers in BMJ Oncology (link here).

Drawing on data from the Global Burden of Disease 2019 Study for 29 cancers in 204 countries, they examined incidence, deaths, disability-adjusted life years (DALYs) and contributory risk factors for all those aged 14 to 49 to estimate annual percentage change between 1990 and 2019.

In 2019, new cancer diagnoses among the under 50s totalled 3.26 million, an increase of 79% on the 1990 figure. Overall, breast cancer accounted for the largest number of these cases and associated deaths at 13.7 and 3.5 out of 100,000 of the global population, respectively.

But new cases of early onset nasopharyngeal and prostate cancers rose the fastest between 1990 and 2019, with estimated annual percentage changes of 2.28% and 2.23%, respectively. At the other end of the spectrum, early onset liver cancer fell by an estimated 2.88% every year.

Some 1.06 million people aged under 50 died of cancer in 2019, an increase of just under 28% on 1990, with the steepest increases in deaths among people with kidney or ovarian cancer.

Multiple myeloma deaths also rose over the 30 years, although deaths from Hodgkin lymphoma and leukaemia fell and non-Hodgkin lymphoma deaths remained steady.

The highest rates of early onset cancers in 2019 were in North America, Australasia, and Western Europe. But low to middle income countries were also affected, with the highest death rates among the under 50s in Oceania, Eastern Europe, and Central Asia.

And in low to middle income countries, early onset cancer had a much greater impact on women than on men, in terms of both deaths and subsequent poor health, the researchers found.

Based on the observed trends for the past three decades, they estimated that the global number of new early onset cancer cases and associated deaths would rise by a further 31% and 21%, respectively, in 2030, with those in their 40s the most at risk.

Genetic factors were likely to have a role, but diets high in red meat and salt, and low in fruit and milk; alcohol consumption; and tobacco use are the main risk factors underlying the most common cancers among the under 50s, they said.

In addition, the data indicated physical inactivity, excess weight, and high blood sugar were contributory factors, according to the authors.

The researchers acknowledged various limitations to their findings: principally, the variable quality of cancer registry data in different countries may have led to under-reporting and under-diagnosis, they suggested.

They also stressed it was still unclear to what extent screening and early life exposure to environmental factors may be influencing the observed trends.

Nevertheless, the study highlighted the changing epidemiological landscape of cancer incidence, wrote public health researchers from Queen’s University Belfast, in an accompanying editorial (link here).

“The findings…challenge perceptions of the type of cancer diagnosed in younger age groups,” they wrote.

“Full understanding of the reasons driving the observed trends remains elusive, although lifestyle factors are likely contributing, and novel areas of research such as antibiotic usage, the gut microbiome, outdoor air pollution and early life exposures are being explored.”

They conclude: “Prevention and early detection measures are urgently required, along with identifying optimal treatment strategies for early-onset cancers, which should include a holistic approach addressing the unique supportive care needs of younger patients.”

“There is a pressing need for partnership, collaboration and resource distribution at a global level in order to achieve these aims.”