More women under 50 are getting breast cancer today than ever before. This is the perception of many doctors. But saying by how much, whether this increase is more or less accentuated than that which occurs in women over 50, how it changes based on the geographical area and what it depends on is not at all simple. And, in truth, there is not complete agreement in the scientific community even on whether the increase is real or just anecdotal, at least as far as Italy is concerned. At the base there is a problem of data availability and, obviously, how they are read.
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In the USA, however, a study was conducted – now published on Jama Network Open – which answers many questions (at least for American women). Epidemiologists at the University School of Medicine in St. Louis (Missouri) asked themselves: what has been the trend in the incidence of breast cancer in women between the ages of 20 and 49 over the last 20 years?
The sample
We used 17 Surveillance, Epidemiology, and End Results Program (SEER) registries, covering approximately 27% of the US population. This is data from over 217 thousand women, between 20 and 49 years old, who developed breast cancer from 2000 to 2019. We are therefore talking about a large sample, in which it was possible to distinguish trends based on characteristics such as the stage of the disease at diagnosis, the state of female hormone receptors, ethnicity and socio-economic status, thus obtaining timely and potentially useful information to direct prevention strategies among women under 50.
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A surge from 2016 to 2019…
Let’s get to the results. The first thing that stands out is that the incidence increased steadily and slightly until 2016, and then increased more markedly in the last three years: the rate was +0.24% per year between 2000 and 2016 and +3.76% per year from 2016 to 2019.
…but not for all
This increase, however, is not observed in all cases. Stratifying based on the disease stages, we only see it for very early or very advanced ones. In detail: the incidence rate increased overall by 3.45% per year for stage I tumors and by 3.39% for stage IV (metastatic) tumors, while it decreased by 3.42% and 3.06% for stages II and III, respectively. “This information is very interesting and allows us to make hypotheses on possible explanations”, comments Diego Serraino, director of the complex operational structure of Oncological Epidemiology of the CRO of Aviano, to Salute Seno.
This is not the only information that, fortunately, the SEER program records collect. It can be seen that estrogen-positive tumors (ER+) have increased, while progesterone-positive tumors (PR-) have decreased. Analyzing the data again by age group at diagnosis (20-29, 30-39, and 40-49 years) and by ethnicity, we see how the increase is more marked among black (non-Hispanic) women in the first two groups older than all the others.
“Our findings on the increased incidence in young women are in line with those of previous research,” the authors write in the study. Which also highlight its limitations, such as the absence of information regarding HER2 receptors (available only since 2010) and the lack of information in the registers on risk factors.
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What the data means
“Despite the limitations, this study is very important – continues Serrino – especially because it takes into consideration an unselected and therefore truly representative population, unlike studies done in a clinical setting. This is the kind of sample that can really tell us something about epidemiology.”
What could explain the observed increase in incidence? “The real leap – replies the expert – is observed starting from 2016. When a curve rises so rapidly, it is reasonable to assume that something has changed in our ability to make diagnoses, for example an improvement in technology or the introduction of a new method”. In essence, tumors that would probably have been discovered a few years later are discovered first: therefore in another age group and in a more advanced stage. “In fact – he continues – the fact that diagnoses have increased very early, stages I, but not stages II and III, could indicate greater attention in young women, perhaps as a consequence of awareness campaigns or for a greater diffusion of genetic tests and greater awareness of tumors linked to BRCA mutations”. The increase in very advanced stages, on the other hand, could reflect the fact that some populations have been less reached by information or – hypothesizes Serraino – have had less opportunity to access early diagnosis in a context in which healthcare is private.
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Again: “For the 20-29 age group it is difficult to think that the causes of this increase are lifestyle or environmental factors, because in both cases the times are too short. On the contrary, for the 40-49 year age group there is the possibility that lifestyles and choices play a role. Breast cancer, particularly hormone receptor-positive breast cancer, has certain risk factors including nulliparity, an age at first child of over 30-35 years, not breastfeeding, as well as alcohol and being overweight. . If the former depend on social conditions, it is possible to act on the others to prevent them. Still few women know, for example, that alcohol is a certain risk factor, recognized by the International Agency for Research on Cancer (IARC). Having said this, it is certainly very complex to make a single synthesis of what has been observed.”
The situation in Italy
And on this side of the ocean? Is there data that would allow us to do a similar study in our country? “It is our intention and we have already requested them from the Italian Association of Tumor Registries – replies the epidemiologist -. For the moment we have them for some areas: Friuli Venezia Giulia, Veneto, Emilia Romagna and a part of the Province of Naples, with the ASL Napoli 3 Register which covers 600 thousand inhabitants”.
Right here we observe a doubling of the incidence rate in the under 50s: it was 30 women out of 100 thousand in 2000 and rose to 60 out of 100 thousand in 2020. In Veneto it was 61 out of 100 thousand in 2007 and rose to 73 out of 100 thousand in 2019. In Emilia Romagna it was 68 women out of 100 thousand in 2006 and rose to 76 out of 100 thousand in 2019. “We are talking about modest increases in incidence, of around 1% per year – underlines Serraino -. Caution, however, when making comparisons between Regions or between age groups: the incidence also depends on the activation or otherwise of screening programs and on the awareness and participation of the female population. For example – he concludes – in Emilia Romagna women have been able to participate in screening from the age of 45 since 2009, while in other regions it still starts from the age of 50″. Under different conditions it is normal for the incidences, and the way in which they change over time, to be different.
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