causes and risk factors

Breast cancer: which women are most affected, is it rare before the age of 40?

Around 61,000 new cases of breast cancer were diagnosed in 2023. The median age of diagnosis is 64 years. “About 5% of these women were under 40 years oldreveals Dr Emmanuelle Mouret-Fourme, doctor specializing in oncogenetics and epidemiology at the Curie Institute. This represents approximately 3,000 women under the age of 40 who are affected by breast cancer.

Breast cancer is therefore rather rare in young women, before the age of 40. Our expert specifies, however, that the incidence of breast cancer has increased slightly in recent years, including among younger people. “The incidence has increased slightly as in other age groups since 2000. The reasons for the recent increase still remain unknown or hypotheses. What we do know is that the earlier a breast mass is detected, autopalpation or by clinical examination, the earlier the cancer is diagnosed, the higher the chances of curing the disease

What are the causes of breast cancer before age 40? Who are the women most affected?

The causes of the occurrence of breast cancer in young women are not yet elucidated. The level of scientific evidence often remains insufficient. “However, we know the strongest risk factors. For others, we can, to date, only suspect them.”

Risk factors can be grouped into 3 categories: individual factors, behavioral factors and environmental factors. These risk factors are not specific to women under 40. They are common to all age groups.

Breast cancer and individual risk factors

Age

Age is the main risk factor for cancer: the older we get, the more the risk increases, particularly after menopause. Around 80% of women affected by breast cancer are over 50 years old.

Family and personal history

“The strongest risk factors we know to date are genetic factors.” However, hereditary predispositions are responsible for approximately 5 to 10% of all breast cancers. These genetic predispositions can favor the onset of the disease at an earlier age. Also, women affected by these genetic predispositions, particularly associated with the BRCA1 or BRCA2 genes, have follow-up that is recommended to start at an early age.

Hereditary predispositions to breast cancer are not responsible for the increased incidence of breast cancer.

Hormonal factors

Exposure to natural hormones is also a moderate but proven risk factor. These include the onset of periods before the age of 11 or late menopause, which can moderately increase the risk. The late age of first pregnancy, which fluctuates around 30 years compared to 25 years in the 2000s, would also be a moderate risk factor. A link is also possible between breast cancer risk and hormone replacement therapy for menopause.

Origin of breast cancer and lifestyle

• Regular consumption of alcohol and tobacco increases the risk of breast cancer. No alcohol is less risky than another. Like alcohol, tobacco and drugs are proven factors that increase risk.
• An unbalanced diet (fast food, insufficient amount of dietary fiber) also plays a role.
• Overweight and obesity are also risk factors for the occurrence of many diseases and cancers, including breast cancer.
• A sedentary lifestyle is also recognized as a risk factor for breast cancer.

The above factors are said to be “modifiable” by changing our lifestyle habits. These factors are also risk factors for other pathologies, such as diabetes or cardiovascular diseases, so by modifying them we help to reduce the future risks of several pathologies.

Personal history and environmental risk factors

Medical exposure to ionizing rays requires specific monitoring of patients. One of the most frequent indications for this medical follow-up is radiotherapy to treat Hodgkin’s disease. The risk of breast cancer is increased in women who received this treatment before the age of 30. Specific monitoring is recommended in this particular context.

Suspected risk factors: diet, pollution, endocrine disruptors, etc.

As with all types of cancer, certain factors could increase the risk, including breast cancer:​​​​​​

Sedentary lifestyle, smoking, late pregnancy… These risk factors are low if taken one by one. Their impact on epidemiology and in particular on the evolution of incidence among young women in France remains to be demonstrated.

“We need to improve our knowledge to know whether combinations of factors could explain this epidemiological situation,” says Dr Mouret-Fourme. In certain women who combine them, the individual risk could indeed be increased, and perhaps early, but this remains uncertain. However, primary prevention remains essential in order to preserve overall health, by reducing these risk factors, which are also involved in diabetes, cardiovascular diseases and other cancers.

Certain diseases (metabolic syndrome for example) and cancers (including breast cancer) are often multifactorial.

At what age can you get breast cancer?

“Breast cancer is rare before the age of 30,” explains Dr Mouret-Fourme.

Current projects: research on this disease in women before the age of 40

An increasing incidence, a decreasing mortality and a better prognosis

If the incidence increases in all age groups, the prognosis of breast cancer improves, with a mortality rate which has decreased over the same period, since 1990. “This improvement is evidence of therapeutic progress and actions screening”.

Improving screening among young women

“However, there remain unknowns regarding the causes of breast cancer in young women and the reasons for the increase in incidence overall and among young women. One of the challenges at the Institut Curie is to improve understanding carcinogenesis”, continues the doctor. “This is why we have just inaugurated theWomen’s Cancer Institutedirected by Professor Anne Vincent-Salomon, with part of the research work which will, among other things, focus on these aspects. We wish to increase efforts to better understand and quantify the impact of hormones and endocrine disruptors in women. These ambitious study projects will begin to better understand the disease, better manage it, improve screening methods and carry out more targeted actions,” concludes our interlocutor.

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