September 6, 2023

expert reaction to study looking at global cancer cases among the under 50s over past three decades

A study published in BMJ oncology looks at the global increase in early-onset cancer cases.

Professor Montserrat García-Closas, Professor of Epidemiology at The Institute of Cancer Research, London, said:

“This paper seeks to address important questions on global surge in early-onset cancers, however, limitations with the methodology make it unclear what these findings add to current literature.

“Previous reports have shown that globally, since the 1990s, there has been an increase in cancer incidence rates in the under 50s and a decrease in mortality rates, meaning more people under 50 are surviving their cancers, likely due to improvements in early detection and treatments.

“The press release focuses on an increase in the global incidence of cancer in under 50s, and an increase in the number of deaths in under 50s between 1990 and 2019. It’s important to note that this statement is based on absolute numbers rather than age-standardised rates, meaning these numbers do not account for changes in demographics such as increases in population size or aging of the population. In their paper the authors report a decrease in age-standardised cancer death rates, in line with previous studies.

“The authors acknowledge that there was large variation in incidence rates, mortality and other measures across regions, countries and cancer types. This makes ‘global’ conclusions difficult and potentially misleading. The authors also acknowledge that there was variation in the quality and availability of data provided by different countries, which makes it difficult to draw accurate conclusions about incidence and mortality, and their relationship to certain risk factors.

“Most countries did not have available data on how the prevalence of risk factors like smoking or obesity changed over time. This would have limited the authors ability to draw reliable conclusions about how temporal trends of these risk factors contributed to cancer incidence or mortality over time.”

Prof Dorothy Bennett, Professor of Cell Biology, St George’s, University of London (SGUL), said:

“This is a global report on “early-onset” cancer, meaning cancer diagnosed in people between 14 and 45 years old.  They report on changes between 1990 and 2019.  It is not possible to comment on the detailed data at present, because they are largely in supplementary online information which we cannot yet access. 

“The press release mentions a “striking 79% increase” in new cases of early-onset cancer over the period. This refers to total numbers rather than rates (or risk) of cancer per person.  The world human population increased by 46% between 1990 and 2019 (Worldometer data), which explains part of the increase in total case numbers, though I don’t know the exact % increase for the 14-45 age group.

“Some changes in some countries may also be due to changes (usually improvements) in reporting, as they note, potentially explaining another part of the increase in reported numbers. The increase in numbers of cancer deaths in this age group was notably lower than for diagnoses, namely 28%, which is below the increases in total population and case numbers, indicating a fall in the average cancer death rate in this group.

“They present a fair amount of data on risk factors for selected cancers that show high global increases in death rate (breast, bowel, stomach): nothing surprising.  Alcohol, smoking, “dietary” etc. The risks are broadly grouped (within the main paper).

“We know that distributions of different types of cancer vary widely between different countries. Regarding the UK, there are no specific comments on UK data in the text, although there are map diagrams showing broad indications of the calculated changes by country. For example, the diagrams indicate that the total number of deaths from this kind of early-onset cancer fell by between 20-60% in the UK, but the age-specific rate of deaths rose by between 20-30%.  This is hard to understand unless the numbers of UK people of this age fell considerably in that period – which they didn’t. So, it would be helpful to know how the calculations were done. This is not made clear, they give equations, but do not define the terms. The total UK population rose by 17% in the period (Worldometer). 

“Anyone interested in UK data on specific cancers and the changes over time could try the CRUK website:  Cancer Statistics for the UK (cancerresearchuk.org).”

Prof Stephen Duffy, Centre Lead, Centre for Prevention, Detection and Diagnosis, Queen Mary University of London (QMUL), said:

“These results are interesting but colleagues will need to give considerable time and thought as to their interpretation. It is interesting that there is a strong decreasing trend in liver cancer incidence, and an increasing trend in nasopharyngeal cancer incidence, since both have large numbers attributable to infectious causes. In the case of liver cancer, large numbers are caused by hepatitis B virus, for which there is effective vaccination whereas for nasopharyngeal cancer, large numbers are caused by the Epstein-Barr virus, for which we do not have effective vaccination. Although this interpretation makes sense, it is speculative, and the real reasons for the trends may be different.

“The finding of an increasing trend of breast cancer incidence in women under 50, is consistent with what is happening to rates in the UK. Since we do not routinely screen women aged under 50, this is not due to increased diagnostic activity due to screening. It also suggests that similar increases over time in women aged over 50 who are offered screening, are not due to screening alone.

“Overall, there are many interesting results here, but they are complicated, and the cancer prevention and control community will need to take a long look at them over the next few weeks to consider exactly what they mean and what we can do to reverse some of the increasing trends.”

‘Global trends in incidence, death, burden and risk factors of early-onset cancer from 1990 to 2019’ by Jianhui Zhao et al. was published in BMJ Oncology at 23:30 UK time Tuesday 05 September 2023.

DOI: 10.1136/bmjonc-2023-000049

Declared interests

Professor Montserrat García-Closas: No COIs

Prof Stephen Duffy: “I have no conflict of interest.”

Prof Dorothy Bennett: “I have no conflict of interest.”

For all other experts, no reply to our request for DOIs was received.