Each year, the International Agency for Research on Cancer (IARC) publishes the incidence of different types of cancer worldwide, by age and gender. This agency, which is linked to the World Health Organisation (WHO), compiles the incidence reports on the basis of information from GloboCan, the International Cancer Observatory, which brings together the national registers of 185 countries.

However, regarding leukaemia, the GloboCan reports merge the different subtypes under one category, which does not allow for a more in-depth analysis of the diversity of leukaemia. This year, for the first time, IARC has promoted an initiative to analyse the incidence of leukaemia considering its full range of typologies. The findings of this report show that there are large differences between countries in the incidence of leukaemia and that the latter also varies between age groups.

Dr. Rafael Marcos-Gragera, head of the Descriptive Epidemiology, Genetics and Cancer Prevention group at the Josep Carreras Leukaemia Research Institute, member of IDIBGI and coordinator of the ICO Cancer Registry, has actively participated in this research, recently published in the prestigious journal Leukemia. Today, he is explaining us the key findings of this report.

What is the main lesson you have learned from this research?

We have observed that the pattern of incidence of leukaemia is totally different in children than in adults. In children, adolescents and young adults, acute leukaemia predominates, while in older people, chronic leukaemia predominates, whether lymphocytic or myeloid.

Is there a biological mechanism that might explain this difference?

Well, acute leukaemia is generally considered to be caused by mutations that can be inherited from parents. That is why it manifests at an early age. Chronic leukaemia, on the other hand, is more closely linked to alterations accumulated over time and more likely to be caused by environmental risk factors.

Do we know which are those risk factors?

That is the million-dollar question! They are not really known, although chronic leukaemia is associated with less healthy lifestyles. Obesity, type of diet or smoking are known to have an impact, but none of them are determinants on their own, as they can be in other types of cancer, such as lung or pancreatic cancer. We are dealing with a set of combined factors. The fact that these factors are not known does not mean that they do not exist, but that more research is needed.

You have analysed international data, are there also geographical differences in the incidence of leukaemia?

Yes, and the main factor is the socioeconomic level of the country. For example, we have seen that chronic leukaemia has a higher incidence in more developed countries. You might think that this is due to their older population, but we have realised that, with regard to chronic leukaemia, what might be happening is that there might be an under-representation of these diseases in the registries of countries with a low socioeconomic status.

Do you mean it ‘flies under the radar’?

Chronic leukaemia often has no symptoms and is detected in routine check-ups. In many cases it does not even require admission and doctors take a watchful, monitoring approach. In countries with poor quality registration systems, these cases are not reported and therefore not registered unless the disease becomes complicated. This is not the first time this phenomenon has been observed and an effort must be made in this direction.

What is the practical use of this information, of knowing which are the most frequent types of leukaemia in each age group?

On the one hand, we can see the evolution of the incidence and plan health resources much better. But we can also see how the new therapies are working. For example, acute leukaemia, which we typically find in young people, is achieving very good cure rates, almost 90-100% in the case of acute lymphocytic leukaemia, which in the past had a very poor prognosis. However, this is not the same everywhere.

And again comes the socio-economic level... right?

Exactly. There are countries that do not have access to new therapies, which are sometimes very expensive, and we don't see this effect on survival. And we don't have to go very far: in Europe, Nordic countries have much higher survival rates for acute lymphocytic leukaemia than other countries of the region, especially in the East, despite having similar incidences.

What about chronic leukaemia?

Right now we see that the new tyrosine kinase inhibitor drugs, such as Imatinib, have transformed chronic myeloid leukaemia, a disease that had a very low survival rate, into a curable disease in most of the cases. We are improving a lot and, both in Catalonia and in Spain, the situation is really good.

How does all this information help in the fight against leukaemia?

With these data that have been published, and taking into account age distribution, if we apply it to the Catalan population we can know, for example, the number of cases of acute lymphocytic leukaemia diagnosed in children, or the number of chronic myeloid leukaemia in adults. The data alone will not give us a solution to cure leukaemia, but we will be able to know how many cases we are talking about and monitor them over time to see how mortality may be changing. This is also one of the goals of epidemiology!

The Cancer Registry does not do basic laboratory research to find a molecule capable of treating patients, but we can monitor how advances in research impact on these indicators, which will help us to know where we are in the fight against leukaemia.

The research was funded by IARC-WHO and the University of Bergen Medical School. No generative AI tools were used in the development of this text.

Reference Article: Dagrun S. Daltveit, Eileen Morgan, Murielle Colombet, Eva Steliarova-Foucher, Karima Bendahhou,Rafael Marcos-Gragera, Zheng Rongshou, Alexandra Smith, Hui Wei and Isabelle Soerjomataram “Global patterns of leukemia by subtype, age, and sex in 185 countries in 2022”. Leukemia, https://doi.org/10.1038/s41375-024-02452-y