More young women are suffering from breast cancer, and doctors are struggling to understand why.
Breast cancer rates in women under 50 have increased more than 15% over the past two decades, an increase that is almost entirely due to the increase in estrogen receptor-positive (ER+) breast cancer. a subtype of tumor that uses the hormone estrogen to grow and spread.
Estrogen receptor-positive breast cancer is the most common in all age groups. Because this specific type of breast cancer is causing an increase almost exclusively in young women, some doctors suspect the trend is related to the fact that more people in the United States are menstruating at an early age and having their first child in late ages.
“Women are exposed to more estrogen throughout their lives,” explains Alexandra Thomas, an oncologist at Duke Health. “That’s probably an important part, but we don’t know why we’re seeing people having their period earlier.”
This increase is likely due to many factors, including obesity, alcohol consumption, genetics, and some hormonal contraceptive methods, but increasing attention is being paid to the role that early puberty plays in breast cancer risk. .
The age at which girls begin puberty has been declining for decades, especially among black and Asian Americans.
“This study is still in an early phase,” says Adetunji Toriola, a molecular epidemiologist at the University of Washington Siteman Cancer Center. “But we do know, from some of our previous work and that of others, that we know certain factors that may be responsible. “We know that these reproductive factors may be related to breast cancers.”
Menstruate earlier, have children later
It has long been known that the onset of puberty at a very young age is linked to an increased risk of developing breast cancer, although there is still little research into how this influences the age at which diagnosis occurs.
A study published earlier this year in the scientific journal JAMA Network Open found that women born between 1950 and 1969 were, on average, 12.5 years old when they had their first period.
Less than 9% had menarche—the term for a girl’s first menstrual period—before age 11, which is considered early. Only 0.6% of these women had their first period before age 9, or very early in their life.
Girls born between 2000 and 2005 had their first period, on average, just before turning 12, half a year earlier than those born 40 to 50 years earlier. Rates of early and very early menarche also increased, to 15.5% and 1.4%, respectively.
“If you start menstruating before age 11, you have a higher risk of breast cancer, and the average age (of menarche) continues to decline,” says Eleonora Teplinsky, chief of breast and gynecologic medical oncology at Valley Health System. in New Jersey.
Studies suggest that for every year younger a girl is at the time of menstruation, her lifetime risk of breast cancer increases by 5%.
Early breast development also increases the risk of breast cancer. A study of nearly 50,000 women found that girls who developed breasts before age 10 had a 23% higher risk of developing breast cancer over their lifetime, compared to those who began developing breasts at age 12 or 13 years old.
When a woman begins to menstruate, her ovaries release estrogen and progesterone. Both can contribute to a woman’s increased risk of developing hormone-sensitive subtypes of breast cancer, which tend to grow more slowly and are easier to treat.
About 75% of breast cancers are sensitive to at least one hormone, usually progesterone or estrogen, according to the American Cancer Society.
At the same time, women are having children later in life, or choosing not to.
Although having a child may temporarily increase a woman’s risk of breast cancer, it slightly decreases the long-term risk, says Ann Partridge, co-founder and director of the Young Adult Breast Cancer Program at Dana-Farber Cancer Institute.
Although a woman stops her menstrual cycle during pregnancy, “it’s not just about how many cycles a person has been exposed to, but also the timing of the pregnancy, which is not related to estrogen,” says Partridge.
Instead, it may have something to do with the changes that occur in the breast after childbirth, when a woman’s mammary glands return to their pre-pregnancy state. This elevated risk is greater among women who have children later.
“Women who have children before age 30 have a lower long-term risk of developing breast cancer,” says Partridge. “We don’t know why, but the older you are when you have your first pregnancy, the greater the risk you have in the short term.”
Partridge adds that it’s not clear why, but it may have to do with younger bodies typically being better at quelling inflammatory responses and repairing damaged DNA.
Why is breast cancer increasing in younger women?
Doctors continue to investigate why breast cancer is becoming more common at a younger age.
“Women do not have children or they have them later. They do not breastfeed as much, which increases the risk of breast cancer. But that doesn’t explain it completely,” explains Teplinsky. “We know that obesity and a sedentary lifestyle contribute, but why are we suddenly seeing this increased risk?”
Teplinsky says more research is needed on the relationship between environmental toxins — such as chemicals known as endocrine disruptors — and breast cancer.
A study published earlier this year in the journal Frontiers in Toxicology found that nearly 200 chemicals linked to breast cancer are used in food packaging, including cardboard. Some recent studies suggest that the use of estrogen-containing contraceptives may slightly increase the risk of breast cancer.
Obesity could be another determining factor in breast cancer diagnoses at younger ages, but making this association is complicated.
Obesity is believed to be one of several factors that can trigger earlier puberty. It can also increase the risk of breast cancer by up to 30%, but research suggests this only occurs in postmenopausal women, especially if the woman also has difficulty regulating blood sugar levels.
According to Toriola of the University of Washington, this would indicate that obesity is probably not a major factor in the increase in breast cancer rates among younger women.
Toriola notes that most research on lifestyle factors and breast cancer is conducted in women of all age groups, making it difficult to identify factors specific to younger women.
She added that more clinics should adopt risk prediction models, such as the Tyrer-Cuzick risk assessment, which take into account more than just a woman’s personal and family history of breast cancer and mutations, and include other factors such as precocious puberty.
“They constitute a holistic view of a woman’s risk of developing breast cancer,” says Toriola. “They take all risk factors into account and would be able to better indicate what actions or tests a woman would need to take.”