Four out of ten cancer cases due to modifiable factors such as tobacco, according to WHO analysis

Is the study based on solid data and methods?

"Yes. Obviously, this estimate is based on a pragmatic approach to obtain global results from all available information. The number of cancer cases worldwide is itself an estimate, as many countries, including ours, do not have cancer registries with national coverage, and in some countries there are no registries at all. Furthermore, as the authors themselves acknowledge, the latency period used (10 years) may not be the most appropriate for all locations and/or all age groups. There are therefore many sources of uncertainty, but the study provides solid information on many of the fully established modifiable cancer risk factors to give an estimate of the percentage of cases that could be prevented if these factors were eliminated.

What new information does it provide?

‘The study expands the list of risk factors considered, uses cancer incidence (not mortality) data and provides, I believe for the first time, estimates for 185 countries in addition to large geographical regions, as well as a comparison of the main preventable factors by tumour type. This effort was led by the IARC. In addition to being up-to-date data, I believe that having this information is very relevant.’

Are there any important limitations to consider?

"The authors discuss the main limitations in the article, some of which have already been mentioned. Perhaps the most important is the impossibility of taking into account the combined effect of different risk factors with synergistic effects, i.e., with a greater effect than expected considering the role of each of these exposures or risk factors. This implies that these estimates are possibly conservative and that the benefit of avoiding these determinants or risk factors would be even greater."

How relevant is this study to clinical practice in Spain?

"The main conclusion of this study is the value of prevention in effectively reducing the burden of cancer on our population. Furthermore, quantifying the effect of each of the factors considered also serves to prioritise efforts in this direction. Clearly, in our context (Figure 3), tobacco, alcohol, infectious agents, obesity and a sedentary lifestyle are the main factors to avoid. It is interesting to note the differences between men and women; in the former, the weight of tobacco is much greater. It is also important to consider factors such as pollution or occupational exposures that cannot be modified individually and must be taken into account in the protective measures proposed by the public authorities."

Is the study based on solid data and methods?

"The study is relevant and its conclusions are important, as it has analysed a huge amount of data by cross-referencing different databases. On the one hand, they analyse the incidence of new diagnoses of different types of cancer by country, age and gender using the GLOBOCAN database; and, on the other hand, they use several databases on the prevalence of known cancer risk factors, including those from the WHO, IARC and UNICEF, from which they extract the risk of exposure to the different known risk factors in that age group, country and gender. By cross-referencing the databases, they can establish which cancers could be prevented by country and gender.

Therefore, the study has a weakness in that it does not establish a cause-and-effect relationship, but rather uses known factors to establish a correlation between cancer prevalence and the proportion of risk factors 10 years earlier in that population.

Given the large number of tumours included—18.7 million, of which 7 million are attributable to preventable cancers—and the power of the databases used, the conclusions can be considered sufficiently robust."

How does it fit in with previous work? What new information does it provide?

"The study highlights the importance of preventable risk factors such as tobacco, infections and others in the development of cancer in the population. What I would highlight about this work is that it quantifies it in figures and that these are really compelling. For example, it clearly highlights tobacco as the leading cause of cancer in men, attributing no less than 23.1% of all cancers in men in 2022 to this cause. This gives us an idea that anti-smoking campaigns or smoking prevention efforts could have a huge impact on cancer control.

The data is equally relevant in the case of women, for whom infections are the main cause of cancer, specifically the papilloma virus (for cervical cancer) and Helicobacter pylorii for gastric cancer. 11.5% of cases could be due to exposure to these agents.

This is very important for designing, justifying and even intensifying efforts in vaccination campaigns against the papilloma virus. This also has greater or lesser consequences depending on geographical location."

Are there any important limitations to consider?

As I mentioned before, the biggest limitation is that it is not a cause-and-effect or case-control study, but rather an epidemiological study in which prevalence data is cross-referenced with exposure to known risk factors by sex, age and country. Despite this limitation, I believe the study is thought-provoking and should be taken into consideration."

How relevant is this study to clinical practice in Spain? What recommendations can we make based on it?

"Given that these are epidemiological data, the greatest applicability is that it clearly quantifies, in a more or less approximate way, the true impact of not taking measures to prevent cancer. Maintaining high levels of exposure to risk factors has consequences. 7.1 million consequences (preventable cancer) in 2022 worldwide.

But it also allows health authorities to be guided as to which countries, genders and locations this lack of prevention has the highest cost.

On the other hand, this quantification is important because it allows us to justify that prevention strategies have an impact on the population and can also be cost-effective, since preventing 7 million cancers by modifying exposure to risk factors not only improves the health of your population, but also significantly reduces healthcare costs."