Why are so many young women getting breast cancer?

Siobhan Donovan is a runner who eats her vegetables, doesn’t smoke and only drinks socially. He had no family history of cancer. So when her breasts swelled near the end of what she called a “textbook easy pregnancy” with her third child, she and her doctors weren’t expecting anything big.

They are wrong. Ms. Donovan, who was 33 at the time, had advanced breast cancer that had spread to her bones.

“I was shocked,” he said, adding that at the time he didn’t even know what the word “metastasis” meant.

Like Ms. Donovan, more and more young women are being diagnosed with breast cancer, according to new estimates released Thursday by the American Cancer Society. Between 2012 and 2021, the overall breast cancer rate increased by about 1 percent per year, while the rate increased by about 1.4 percent per year the case of women under 50 years of age. Patients with “young breast cancer” – which doctors generally define as having the disease before the age of 40 – are more likely than older patients to develop aggressive forms of breast cancer. the disease, said Dr. Ann Partridge, interim chair of medical oncology at Dana. – Farber Cancer Institute in Boston.

The increase in breast cancer rates among young patients is occurring as the incidence of other cancers – including colorectal, stomach, kidney and liver cancer – is also increasing, although Cancer is still rare in patients under the age of 50, Dr. .

By 2024, there will be fewer than 51,000 new cases of breast cancer in women under 50, compared to 260,000 cases among women 50 and older, according to data from number American Cancer Society.

“Cancer is a disease of old age,” said Dr. Partridge. “But if you get cancer in your 30s or 40s, if you’re a woman, it’s more likely to be breast cancer.”

Researchers do not know what causes the increase in breast cancer. Although mammography screening has increased in the detection of breast cancer and breast cancer mortality has decreased, it is unlikely that this is the reason for the increased incidence in younger women, said the expert. The reason is that prevention guidelines have historically not recommended routine mammograms until women are at least 40 years old, so earlier cancers may not be detected through screening. (Last year, the United States Preventive Services Task Force lowered the recommended age to start screening to 40, from 50, in part because more women in their 40s are diagnosed with disease.)

Instead, doctors and epidemiologists believe that the increase is driven by a combination of fertility and environmental or lifestyle changes.

Dr. Adetunji Toriola, a professor of surgery at Washington University School of Medicine in St. Louis, examined the incidence of breast cancer among women under 50 years of age by race, stage, and type. He found that the increase in the last 20 years was driven by breast cancers fueled by the sex hormone estrogen — like the kind Ms. Donovan had.

Breast cells have estrogen receptors, and estrogen helps with cell growth and development. “It’s like fertilizer,” said Dr. Graham A. Colditz, an epidemiologist and director of prevention and control at the Alvin J. Siteman Cancer Center at the University of Washington. But too much estrogen throughout life can lead to the formation and growth of cancer cells.

Over time, there have been population changes that affect a woman’s lifetime exposure to estrogen, which can increase breast cancer rates in all age groups. , experts say.

For example, the average age of girls getting their first period has decreased over the last 60 years. Meanwhile, women enter menopause later, said Dr. Toriola. Both of these changes increase estrogen exposure throughout a woman’s life.

Pregnancy can have different effects at different stages of life. In the short term, pregnancy can increase the risk of breast cancer. But pregnancy, especially before the age of 30, and breastfeeding both have long-term protection against breast cancer later in life – an effect thought to be due to changes in the These are the cells of the breast, said Dr. Partridge. As more women delay pregnancy or choose not to have children at all, this protection may be lost.

Alcohol use, especially in childhood and adolescence, increases the risk of breast cancer. Alcohol can damage DNA and is linked to estrogen exposure, experts say. This is of particular concern because women drink – and drink heavily – at the same rate as men, says Dr. Colditz.

Changing your diet and reducing physical activity can also increase your risk of breast cancer. Many researches, including Dr. Colditz, suggested that the height of women and the growth rate of women are associated with an increased risk of breast cancer, which indicates the impact of nutrition on children.

Research has also shown that exercise reduces the risk of breast cancer, independent of the effect on weight or body mass index, said Dr. Colditz.

Obesity appears to have a mixed effect, increasing the risk of breast cancer in postmenopausal women but reducing it in premenopausal women. But weight gain – independent of physical parameters – has been linked in many studies to an increased risk of breast cancer in women under 50.

Although most breast cancers in younger women, as in older women, are hormone-related types, younger women are more likely to develop breast cancer. more difficult not related to estrogen, such as “triple-negative”. breast cancer, said Dr. Mariya Rozenblit, assistant professor of medical oncology at Yale School of Medicine. They are more likely than older women to have cancer-causing genetic variants such as BRCA1 or BRCA2, although such genetic predispositions still account for cancer in this age group.

Younger women are also not screened as often, so by the time they have symptoms and get the disease, all tumors may be larger and spread more quickly, said Dr. Rozenblit.

Because of the risk of more severe disease, younger women on average have a lower survival rate than older women, Dr. Partridge – although overall breast cancer survival continues to improve with new treatments and shorter delays in diagnosis.

“There is a disparity, but most young women will survive in the short and long term,” said Dr. Partridge.

It has been almost three years since Mrs. Donovan was first seen. He returned to work as a public school teacher in Worcester, Mass., and ran the Boston Marathon in 2024. But his initial chemotherapy and treatments were not enough to stop the cancer, and he had to start treatment. a new drug that leaves him feeling tired and sick all the time. Her youngest son had never seen her full of hair. She recently had her first difficult breast cancer conversation with her 5-year-old daughter.

“At first I never thought I would see three years,” he said. “And even if it’s hard, I’m still going.”