Precocious puberty may contribute to rising breast cancer rates among young women

Caitlin Sullivan and Marina Kopf: NBCNews

More young women are suffering from breast cancer, and doctors are trying to understand why.

Over the past two decades, the incidence of breast cancer in women under 50 years of age has increased by more than 15%, and this increase is almost entirely due to an increase in the number of estrogen receptor-positive (ER+) breast cancers, the subtype of tumor for which breast cancer is used to treat hormone estrogen. grow and spread.

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Estrogen-positive breast cancer is the most common in all age groups. Because this particular type of breast cancer is causing an increase in incidence 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 later in life.

“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 see people getting 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 research is still in its early stages,” says Adetunji Toriola, a molecular epidemiologist at the University of Washington Siteman Cancer Center. “But we know from some of our previous work and the work of others that we know of certain factors that may be responsible. “We know that these reproductive factors may be associated with breast cancer.”

Menstruation earlier, children later

It has long been known that hitting puberty at a very young age is associated with an increased risk of developing breast cancer, although there is still little research into how this affects age at diagnosis.

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 girls’ first 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 life.

Girls born between 2000 and 2005 on average had their first period shortly before they turned 12, six months earlier than those born 40 to 50 years earlier. The incidence 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 (menarche) continues to decline,” says Eleanor Teplinsky, chief of breast and gynecologic medical oncology at Valley Health System in New Jersey. .

Research shows that for every year a girl is younger at the time of her period, her risk of developing breast cancer during her lifetime 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 started developing breasts at age 12 or 13 years old.

When a woman begins to menstruate, her ovaries release estrogen and progesterone. Both may contribute to a woman’s increased risk of developing hormone-sensitive subtypes of breast cancer, which tend to grow slower and are easier to treat.

According to the American Cancer Society, about 75% of breast cancers are sensitive to at least one hormone, usually progesterone or estrogen.

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At the same time, women are having children at a later age or choosing not to.

Although having a child may temporarily increase a woman’s risk of breast cancer, it slightly reduces the long-term risk, says Anne Partridge, co-founder and director of the Young Adult Breast Cancer Program at Dana-Farber Cancer Institute.

Although a woman’s menstrual cycle stops during pregnancy, “it’s not just how many cycles a person has had, but also the timing of the pregnancy, which is not related to estrogen,” Partridge says.

Instead, it may be due to changes that occur in the breasts after childbirth, when a woman’s mammary glands return to the state they were in before pregnancy. This increased risk is higher among women who have children later.

“Women who have children before age 30 have a lower long-term risk of developing breast cancer,” Partridge says. “We don’t know why, but the older you are at the time of your first pregnancy, the higher the risk in the short term.”

Partridge adds that it’s unclear why, but it may be because younger bodies tend to be better at suppressing inflammatory responses and repairing damaged DNA.

Why is breast cancer increasing in young women?

Doctors continue to research why breast cancer becomes more common at younger ages.

“Women do not give birth to children or give birth to them later. They don’t breastfeed as often, which increases their risk of breast cancer. But that doesn’t explain it completely,” explains Teplinsky. “We know that obesity and a sedentary lifestyle contribute to this, but why are we suddenly seeing an increased risk?”

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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 about 200 chemicals linked to breast cancer are used in food packaging, including cardboard. Some recent studies suggest that using estrogen-containing contraceptives may slightly increase the risk of breast cancer.

Obesity may be another determining factor in breast cancer diagnosis at a younger age, but the link is difficult to establish.

Obesity is thought to be one of several factors that can trigger earlier puberty. It can also increase the risk of breast cancer by 30%, but research suggests this only occurs in postmenopausal women, especially if the woman also has difficulty regulating her blood sugar.

This indicates that obesity is probably not a major factor in the increased incidence of breast cancer among young women, said Toriola of the University of Washington.

Toriola notes that most research on lifestyle factors and breast cancer is conducted among women of all age groups, making it difficult to identify factors specific to younger women.

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She added that more clinics should adopt risk prediction models such as the Tyrer-Cusick risk score, which take into account not only a woman’s personal and family history of breast cancer and mutations, but also include other factors such as precocious puberty.

“They provide a holistic view of a woman’s risk of developing breast cancer,” Toriola says. “They take into account all the risk factors and will be able to better indicate what actions or tests a woman needs to take.”