The number of younger women diagnosed with breast cancer has been increasing, a trend that has doctors and researchers working to understand why. 

The past 20 years have seen a more than 15% increase in the incidence of breast cancer among women under 50. A particular kind of breast cancer that is driven by the hormone estrogen, known as estrogen receptor-positive (ER+) breast cancer, is largely increasing.

Since this type explains nearly all of the rise in instances among younger women, researchers believe the trend may be related to changes in reproductive patterns, as more women are starting menstruation earlier in life and delaying the onset of their first children.

Estrogen receptor-positive breast cancer, the most prevalent form in all age groups, is particularly noteworthy because of its reliance on estrogen links it to hormone exposure over time. 

This suggests that changing in the timing of significant life events, such as puberty and childbirth, may be contributing causes. 

Dr. Alexandra Thomas, a medical oncologist at Duke Health, said one possible contributing cause is that many women are now exposed to estrogen for longer periods of time throughout their live. she points out, there is still much to learn about why puberty appears to be occurring sooner, which is a crucial topic of research.

Breast cancer risk may also be influenced by a wide range of other factors, including genetic predisposition, alcohol use, obesity, and certain hormonal contraceptives.  

Many other factors, such as obesity, alcohol consumption, genetic predisposition, and certain hormonal contraceptives, could also play a role in breast cancer risk. 

Among these factors, early puberty has been gaining particular attention for its connection to breast cancer risk. Over the years, the average age at which girls begin menstruating has dropped, especially among Black and Asian American populations. 

Dr. Adetunji Toriola, a molecular epidemiologist at Washington University’s Siteman Cancer Center, mentions that early research indicates reproductive factors have a clear connection to breast cancer risk.

Historically, early onset of puberty has been known to correlate with a higher risk of developing breast cancer later in life. However, less is known about how it may affect the age at which women are diagnosed. 

A study published in JAMA Network Open examined changes over time in the age of first menstruation among American women. It found that women born between 1950 and 1969 had their first period at an average age of 12.5 years, with fewer than 9% experiencing menarche (the medical 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, classified as “very early.”

In comparison, girls born between 2000 and 2005 began menstruating on average just before turning 12, a full six months earlier than girls born 40 to 50 years prior. 

Additionally, the rates of early and very early menarche rose, with 15.5% experiencing it before age 11, and 1.4% before age 9. 

Dr. Eleonora Teplinsky, who leads breast and gynecologic medical oncology at Valley Health System in New Jersey, highlights that the younger a girl is when she begins menstruating, the higher her lifetime risk of developing breast cancer. 

For every year younger a girl is at menarche, her breast cancer risk rises by approximately 5%. Early breast development also plays a role; a study tracking nearly 50,000 women found that girls who developed breasts before age 10 had a 23% greater chance of developing breast cancer in their lives compared to those who began breast development at age 12 or 13.

When menstruation starts, a girl’s ovaries begin releasing estrogen and progesterone. Both hormones are linked to an increased risk for certain breast cancer types that respond to these hormones, including ER+ breast cancer. 

According to the American Cancer Society, about 75% of breast cancers are hormone-sensitive, meaning they respond to either estrogen or progesterone. These hormone-sensitive cancers tend to grow more slowly and are generally easier to treat, but the long-term exposure to estrogen that results from early puberty could increase risk.

Another major lifestyle shift affecting breast cancer risk is the trend of later motherhood or not having children at all. While giving birth can temporarily increase breast cancer risk, it lowers the long-term risk slightly, explains Dr. Ann Partridge, co-founder and director of the Program for Young Adults with Breast Cancer at Dana-Farber Cancer Institute. 

Pregnancy halts the menstrual cycle, temporarily reducing a woman’s estrogen exposure. However, Dr. Partridge notes that the timing of a first pregnancy seems to matter. 

Younger women may be better equipped to handle the stress of pregnancy and the tissue changes in the breast afterward, and this could lower long-term breast cancer risk. On the other hand, women who have their first child after age 30 have a higher breast cancer risk in the short term.

The reasoning isn’t entirely clear, but Dr. Partridge suggests it could involve how younger bodies manage inflammation and repair damaged DNA more effectively. 

After giving birth, a woman’s breast tissue undergoes significant changes, as the mammary glands return to a pre-pregnancy state. This post-pregnancy adaptation could play a role in the breast cancer risk seen in older first-time mothers, although more research is needed to understand this fully.

Despite knowing some of the factors, doctors are still exploring the bigger picture of why breast cancer is becoming more prevalent at a younger age. “There are complex changes in lifestyle,” Dr. Teplinsky points out. 

“Women are either delaying or not having children and breastfeeding less, both of which can increase breast cancer risk. But that doesn’t cover all the reasons we’re seeing this rise.” 

This trend may also be influenced by exposure to certain environmental toxins, such as those found in food packaging and other consumer goods, as well as other risk factors including obesity and sedentary lifestyles.

According to recent studies, breast cancer risk may be impacted by specific chemicals, particularly those referred to as endocrine disruptors. Nearly 200 chemicals used in food packaging, including materials like cardboard, have been connected to breast cancer, according to a study published earlier this year in *Frontiers in Toxicology*.

Although the extent of the danger and its importance are still under study, there is evidence that estrogen-only birth control may marginally raise breast cancer risk.

Obesity plays a complex function in early-stage breast cancer instances. In postmenopausal women, obesity increases breast cancer risk, raising the risk by as much as 30% in some cases. 

Dr. Toriola points out that the increase in breast cancer among younger women is probably not being caused by obesity. It is unclear how obesity affects premenopausal breast cancer, although it does lead to an earlier onset of puberty, which is associated with an increased breast cancer risk. Obesity and trouble controlling blood sugar levels appear to increase the risk of breast cancer in postmenopausal women.

It is challenging to identify particular risk factors that specifically affect younger women because the study on lifestyle variables and breast cancer frequently includes women of all ages, according to Dr. Toriola.

He says that in order to find breast cancer risk factors, medical professionals would find it useful to use more thorough risk assessment models, like the Tyrer-Cuzick model.

This model takes into account more than just a woman’s genetic mutations and personal or family history of breast cancer. It provides a more comprehensive picture of breast cancer risk by taking into account a variety of variables, such as early puberty, reproductive history, and other lifestyle impacts. Young women may use this information to make better decisions about tests and preventative measures.

In conclusion, the rising incidence of breast cancer in younger women is a complicated problem that probably involves a number of interrelated causes, including exposure to hormones, timing of reproduction, changes in lifestyle, and even environmental factors.

Although many of these elements are known to elevate risk, the reasons for the recent rise in younger women’s cases are still under investigation. By using more holistic risk assessments and continuing research into these trends, doctors hope to better understand—and eventually mitigate—this disturbing pattern in breast cancer diagnoses.