Breast cancer in young women has increased by 29% in three decades

Something is changing in breast cancer: it remains the most common tumor among women, but risk profiles are not the same. This group of diseases continues to be closely linked to aging, and in fact, most diagnoses occur in women over 55; however, in recent decades, cases in premenopausal women have been increasing more rapidly. A study published this Monday in The Lancet Oncology reveals that, while the rate of new diagnoses in older women has not changed substantially in the last three decades, in women between 20 and 54 years old it has increased by 29% since 1990.

According to the research, which provides an overview of the breast cancer situation in more than 200 countries, 161 new cases per 100,000 women over 55 were diagnosed in 2023. This is three times higher than the number diagnosed among women aged 20 to 54 (50 new cases per 100,000). The interpretation is that age remains a key factor in the risk of developing breast cancer, but by broadening the focus and observing the trend of recent decades, scientists have discovered that diagnoses among younger women, while far fewer, are increasing at a faster rate.

The researchers don’t delve deeply into the causes of this shift, but for oncologists like Gemma Viñas, head of the Breast Cancer Unit at the Catalan Institute of Oncology in Girona, in northeastern Spain, the data aligns with what they observe in their practice: “The incidence is increasing in all age groups, but we are seeing a greater increase in young women.” Isabel Echavarria, scientific secretary of the Spanish Society of Medical Oncology, agrees: “There is evidence that the incidence is increasing in young women, and this is something that worries us oncologists.”

The reasons behind this phenomenon are, to a large extent, still a mystery. Viñas asserts that there is probably “an impact from changes in reproductive factors,” such as the earlier onset of menstruation or the delay in motherhood and the number of children (breastfeeding and pregnancies are protective factors). Other modifiable risk factors, linked to lifestyle, such as being overweight or alcohol consumption, may also be playing a role, she suggests. “In young patients, we don’t know the real cause. It’s probably the sum of many factors,” she hints.

This isn’t the first time science has observed a rise in cancer, a disease traditionally associated with aging, among young adults. According to a study published in the journal BMJ Oncology in 2023, tumors in people under 50 have increased by almost 80% in three decades. Colon cancer is the most paradigmatic, and the one where this emerging trend has been most studied, but it’s not limited to that: it has also been observed in endometrial, kidney, thyroid, and breast cancer, among others. The scientific community is intrigued and has yet to fully define the scope of the phenomenon—some studies find this trend in 13 tumors, others reduce it to half a dozen—but many experts attribute it to the rise in unhealthy lifestyle habits, such as smoking, a poor diet, and being sedentary.

The environment in which an individual grows up could be key. Even before birth, as some experts suggest that exposures in utero can lead to molecular alterations that influence susceptibility to disease. In this regard, some studies suggest that reproductive factors (age at menstruation onset, whether or not breastfeeding was received, fertility rate, use of oral contraceptives, and more), as well as smoking, eating habits, alcohol consumption, lifestyle, and pre-existing conditions of the mother during pregnancy, “could be relevant intrauterine exposures.”

Breast cancer in young women also tends to be more aggressive, Viñas points out. “[This patient profile] usually has more proliferative tumors, and the diagnosis is usually made at more advanced stages because they are not part of screening programs,” she explains.

Echavarria adds that the lack of awareness about the possibility of developing cancer at these ages also contributes to the problem, leading to delays in seeking medical attention. “Furthermore, breast cancer screening tests, such as mammograms, are less sensitive in young women because they have denser breasts, making it more difficult to detect a tumor,” this oncologist explains. However, the rise in breast cancer cases at younger ages has encouraged European guidelines to recommend lowering the starting age for screening from 50 to 45 years.

Inequalities between countries

Beyond this specific phenomenon that keeps the scientific community on alert, the study in The Lancet Oncology also reviews global trends in breast cancer and estimates that in 2023 there were 2.3 million new cases of this tumor and 764,000 women died from this cause.

However, the data reveals that there are several worlds within the same planet. In wealthy countries, where there has been “success in detection, diagnosis, and treatment,” the authors say, the incidence remains stable and mortality rates are declining (five-year survival rates are between 85% and 90%). In contrast, lower-income regions are experiencing an explosion of new diagnoses, and due to deficiencies in their healthcare systems and limited (or nonexistent) access to top-tier diagnostic and therapeutic resources, mortality rates are also skyrocketing (one study in Africa placed the three-year survival rate at 50%).

According to the authors, in a scenario of population growth and aging, the forecast for 2050 across the globe is that new diagnoses will grow by a third (to 3.5 million) and deaths will increase by 44% (to 1.4 million), but the effect will not be homogeneous across the planet: they predict that there will be “a disproportionate impact on countries with limited resources.”

Modifiable risk factors

Researchers are calling for “immediate and decisive action” to address the growing inequalities across the globe and are urging resources to close the diagnostic and treatment gap. They also emphasize the significant role of modifiable risk factors: according to their calculations, more than a quarter (28%) of the global burden of breast cancer—that is, years of life lost due to poor health or premature death—is linked to modifiable risk factors such as smoking, high blood sugar, obesity, sedentary lifestyles, and alcohol consumption.

The authors believe that while some changes in reproductive factors mean fewer women benefit from the protective effect of childbirth, “these changes are unlikely to be the main drivers of breast cancer incidence.” They add, “Instead, the steady increase in exposure to other risk factors, such as early menarche [the onset of menstruation], late menopause, and increased obesity, could result in stable trends in breast cancer incidence by offsetting improvements in exposure to other risk factors, such as alcohol and tobacco use.”

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition