Rising breast cancer in young women

The incidence of early-onset breast cancer has been steadily rising. The reason for this appears to be an increase in menstrual cycles: girls now get their periods around age 11 or 12—slightly earlier than those born in the 1950s; the average age of first pregnancy, when menstruation ceases, is now 27 ½, up from the early 20s in the 1950s. This longer time between first period and first pregnancy—allowing for more menstrual cycles—may be one reason that breast cancer rates are rising in young women.

With every menstrual cycle, breast cells expand, proliferate and contract. The more menstrual cycles, the more opportunities for mutations to arise. During the interval between first period and first pregnancy, cells are more susceptible to harmful exposures such as radiation or alcohol. When women are in their 20s, damage to their DNA is particularly dangerous because they have a lifetime to accumulate mutations.

During pregnancy and breastfeeding, the number of immune cells increases in the breast, offering protection against potentially cancerous cells. After a baby weans, the mother’s milk cells die and get cleared by the immune system, leaving fewer mutated cells behind. The cells that remain spend more time repairing DNA.

With societal shifts to later first pregnancies and fewer babies, women are subject to the potential harms of these natural processes for longer—and get fewer of the protective benefits.

While I’m not concerned about breast cancer for myself, I thought this information was interesting, partly from a societal standpoint, but also because it demonstrates the complexity of the body’s natural healing processes and how they can be disrupted.

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