More and more breast cancers are reported: why?

On the other hand, young women (under 40) are not “increasingly” affected, as is sometimes said. The number of breast cancers in these younger women has indeed increased, but one cannot conclude that breast cancer affects twice as many younger women today as it did 30 years ago, simply because the total number of new cases has also doubled. Seven percent of breast cancers are found in women under 40 years of age, and this percentage has been stable over the past 30 years.
Why has the number of breast cancers doubled? A presentation by Dr. Florence Molinié, research director and epidemiologist at the SIRIC (Site of Integrated Research on Cancer) of Nantes-Angers, at the 2019 congress of the French Society of Senology and Breast Pathology (SFSPM), brilliantly illuminates this evolution of our society. It shows very clearly that the increase in breast cancer rates is linked to a set of changes in women’s behavior, all of which are pointing to the same direction.

Having children and breast cancer

First of all, women today are having their first child later: in 1967, only 12% of women after 30 years of age; in 2015, they were 40%. Having a child early in life protects against breast cancer: this has been formally demonstrated at the population level. Secondly, the number of children per woman has also decreased over the last few decades: in France, for example, it was 3 children per woman in 1950 compared to 1.9 today. Again, on a population level, the more children a woman has, the less likely she is to develop breast cancer. This does not mean that if you have six children, you cannot get breast cancer. But if you take 10,000 women who have had six children and compare them to 10,000 women who have had only one child, you will see slightly fewer breast cancers in the group of mothers with large families. The same is true for breastfeeding, which has a protective effect.

First menstruation and breast cancer

Another key factor is the age of your first period. The later your period is, the less you are stimulated by estrogen during your life, and the lower is your risk of breast cancer. If we take the example of France, the average age of the first menstrual period was 15 years in 1850, it is 12.6 years today.
Obesity in women and breast cancer
Another major parameter is the obesity-breast cancer link. Obesity rates are skyrocketing: they have more than doubled in much of the world since 1980. Obesity is a major risk factor for breast cancer – it is estimated that 10% of breast cancers occurring after age 50 are related to overweight.
Dr. Molinié concludes that it is very likely that the increase in breast cancer rates that we have been observing for decades is the result of behavioral changes related to women’s changing lifestyles. These factors may be environmental or reproductive, but one thing is certain: the steady increase in breast cancer is not related to any one parameter, whether it’s diet, pollution or any other new cancer deity. It is multifactorial.