Breast cancer mortality in Spain has fallen by more than 40% over the last three decades

I believe that the most noteworthy aspect of this article is the effort to provide data for everyone on the leading cancer in women, focusing not only on indicators such as incidence and mortality, but also addressing the burden that this disease represents in terms of years of life lost and years of life lived with disability. The methods used have been developed by GBD and involve a series of assumptions and generalisations that may not be entirely appropriate for particular cases. As an example, the estimated number of breast cancer cases for Spain in 2023 according to this article is 29,400, with an uncertainty interval ranging from 24,600 to 34,400. The SIEC (Spanish Cancer Information System), based on data from existing tumour registries and the methodology developed by the IARC, provides an estimate for the same year of 35,540. In other words, it appears that GBD is underestimating the number of cases in our country. With regard to mortality, the information available in Spain (this is not an estimate, as we have actual data for the whole country) shows that in 2023, 6,405 women died from this cause, a figure clearly lower than that provided in this study (7,890). Despite this variability, I believe the article is important for the reasons mentioned above: it highlights the burden of disease of this tumour, which is a public health problem worldwide, the different life expectancy of women with this disease in higher- and lower-income countries (incidence is higher in countries with a high economic level and mortality is lower), and it also shows the role of some of the modifiable risk factors.

The Global Burden of Disease (GBD) study is one of the largest and most ambitious scientific projects designed to quantify the loss of population health worldwide. This project is led by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington (USA), which is an independent research centre involved in highly rigorous research. This type of study has the limitation that it partly collects retrospective data; in fact, its approach is considered retrospective and longitudinal, examining past data and modelling trends based on that data with current data, allowing even future scenarios to be projected.

The article published in The Lancet Oncology is part of the IHME's GBD study and provides global data on one of the pathologies included in the GBD study, breast cancer, and provides data collected in 2023, comparing it with the previous period since 1990.

The large amount of data analysed and the rigour of the statistical treatment make this a scientifically very solid article. The data provided by this study are very important parameters for understanding how breast cancer affects the population and also compares them by country or group of countries.

To understand the article, it is important to understand the concepts it explains:

• Incidence (the frequency of new breast cancer diagnoses over a period of time) is explained as adjusted for age range, the concept being Age-Standardised Incidence Rate (ASIR). The higher the rate, the more breast cancers are diagnosed.
• The second concept is Age-Standardised Mortality Rate (ASMR), which is self-explanatory.
• Finally, Disability-Adjusted Life-Years (DALY) are a measure of how much harm a disease does to the population. It is the number of years lost due to premature death from the disease + the number of years lived with “disability” —that is, the years in which the person, due to symptoms or toxicities, cannot act or work normally. Thus, if a patient is diagnosed with breast cancer at age 45 and lives from age 48 to 51, but with a poor quality of life, and finally dies at the age of 51, the DALYs would be the 3 years living with disability + X years for premature death, subtracting the age of death from the life expectancy in that country (if it were 81 years, it would be +30 potential years of life lost).

In addition, the study looks at the causality of which risk factor may have had the greatest impact on the loss of DALYs.

The conclusions of the study are very provocative.

In 2023, an estimated 2.3 million new cases of breast cancer were diagnosed and some 764,000 deaths occurred. Breast cancer was the leading cause of potential years of life lost or years lived with disability (DALYs). The estimate of DALYs was 24.1 million years.

However, there are clear differences between different countries around the world:

• In less developed or poor countries, the incidence (ASIR) is lower but mortality is higher, reflecting the importance that mammography screening, access to treatment and the quality of the healthcare system can have on the health of the population. The problem is striking because the incidence (ASIR) in these poor countries has skyrocketed from 1990 to 2023, increasing by 147%. In addition, mortality (ASMR) in poor countries also increased by 99.3%, as did DALYs.
• In richer or more developed countries, the incidence is practically stable (an average increase since 1990 of only 1.2%), but what is most striking in rich countries is the enormous decline in mortality (ASMR), with a reduction of 29.9% since 1990.

The data for Spain provided in this publication speak very well of our healthcare system and its strategy in the fight against breast cancer between 1990 and 2023. Although during this period the incidence in our country increased by 65.5% in new cases of breast cancer (with the incidence rate standing at 65 new cases per 100,000 inhabitants per year), the good news in our country is that, in contrast, mortality decreased by 41.9% over the same period. This decrease is even higher than the average decrease in wealthy countries. The fact that there are many more new cases and yet mortality has fallen by almost 42% in the same period is a major health milestone for which we should congratulate ourselves (see table on page 309 of the publication).

These data show a clear difference in the evolution of this disease depending on the country and its socio-economic situation in terms of how it is managed. This study confirms that the health efforts made in European countries, including Spain, have a positive impact on the health of the population.

In addition, the study establishes a relationship between risk factors and impact in terms of DALY rates: dietary factors, smoking and high plasma glucose levels were the factors that accounted for a 28.3% impact on DALYs (i.e., exposure to these factors increases the risk of years of life lost or lived with disability due to breast cancer by 28.3%). Other factors such as obesity, high alcohol intake, and a sedentary lifestyle also have an impact, albeit to a lesser extent.