Rates of breast cancer — the second leading cause of cancer deaths in U.S. women — climbed by 1 percent a year from 2012 to 2021, and even more sharply among women under age 50 and among Asian American/Pacific Islander women of all ages, according to an American Cancer Society report published on Tuesday.
The biennial report is among the most comprehensive and detailed studies of breast cancer occurrence over recent years. One in 50 U.S. women will develop invasive breast cancer by the age of 50, the authors said, based on National Cancer Institute calculations.
The sharpest increases in young adults by age during the decade were among women in their 20s, whose rate increased by about 2.2 percent a year, though their absolute risk remains very low, at about 6.5 per 100,000 women.
Among Asian American/Pacific Islander women, who historically also have had a low prevalence of the disease, rates increased by 2.7 percent a year among those under 50, and by 2.5 percent a year among older women.
Cancer is generally considered a disease of aging, and that hasn’t changed: The vast majority of breast cancer cases and deaths still occur among older women. But the new study is one of several documenting a troubling uptick in malignancies among younger Americans.
These so-called early-onset cancers pose special challenges. Striking in early adulthood or midlife, they tend to be aggressive yet are often missed because they are not expected, and routine screenings are aimed at older adults.
That has been changing somewhat. Earlier this year, the U.S. Preventive Services Task Force lowered the age for initiating mammography to 40 from 50, reversing an earlier decision to raise the screening age. The American Cancer Society recommends starting annual mammography screening at 45 for women at average risk, with the option of starting at 40.
Despite the rise in incidence, deaths from breast cancer have plunged, dropping by about 10 percent in the last decade and by 44 percent in the past three decades because of improved screening and treatments.
But the benefits have not accrued equally to all women, according to the report, which was published in CA: A Cancer Journal for Clinicians.
Survival rates did not change at all for Native American and Alaska Native women. Breast cancer continues to be the leading cause of cancer deaths among Black women, who have a 38 percent higher death rate than white women.
Black women are more frequently diagnosed with certain kinds of tumors that are more difficult to treat. A recent Mass General Brigham study found that Black women are also more likely than white women to die of all types of breast cancer, suggesting that other factors are playing roles, like delays in diagnosis and difficulty finding timely quality care.
“The bottom line is, we need to improve access to high-quality screening and high-quality treatment for all women of color, especially to Black and Native American women,” said Rebecca L. Siegel, an epidemiologist at the American Cancer Society and senior author of the report. “We need to expand that progress to all women.”
Some 310,720 new cases of invasive breast cancer will be diagnosed in U.S. women this year, including 13,180 cases in women under 40 and 37,650 in women in their 40s, the paper estimated. In addition, 56,500 cases of noninvasive ductal carcinoma in situ will be diagnosed in women of all ages.
An estimated 42,250 women will die of breast cancer, according to the study. Some 2,790 cases will be diagnosed in men, and 530 will die of it.
Breast cancer incidence rose by 1 percent a year overall from 2012 to 2021. But women in their 20s, 30s and 40s experienced a 1.4 percent annual increase in incidence, while the increase among women 50 and older was more moderate, at 0.7 percent each year, the report found.
Getting a diagnosis often takes longer in younger women, leading to delays in treatment and more advanced disease.
After Traci Delaney discovered a hard mass in her right breast, her insurance initially rejected an imaging scan ordered by her doctor. Ms. Delaney, 34, said she herself did not feel particular urgency because she was young and had no breast cancer in her family. (In fact, most women diagnosed with breast cancer do not have the cancer in their family.)
“The biggest thing I realized during this whole entire process is that there’s no age limit on this,” said Ms. Delaney, who lives in Los Angeles and is in remission after treatment last year with chemotherapy, radiation and surgery for Stage II breast cancer. “Maybe there used to be, but I really feel there isn’t anymore.”
It took even longer for Jeanelle Adams, 36, who is Black and Puerto Rican, to be diagnosed with triple-negative breast cancer, a subtype that is especially hard to treat because it is not driven by estrogen, progesterone or another hormone, human epidermal growth factor 2.
Her first symptoms were unusual: a rash on the left breast, which had a dimpled appearance (“like an orange”), and fluid leaking from the nipple. Doctors thought it was eczema, and getting the right diagnosis took Ms. Adams two years, even though she was convinced that something more serious was going on.
Like many other women, Ms. Adams, who is married and lives in North New Jersey, does not have the typical risk factors. She has a 10-year-old daughter whom she breastfed for more than two years; she eats lots of vegetables, has always been physically active and is not overweight.
She suspects environmental factors are at play, though research is sparse. “I work out constantly, I don’t put chemicals in my hair,” she said.
Among women of all ages overall, localized cancers — invasive tumors that have not spread beyond the breast to other parts of the body — accounted for most of the increase in incidence.
Most of the increase was in tumors fueled by the hormones estrogen or progesterone. Among women under 50, the rates increased for diagnoses at every stage of cancer.
Changes in women’s reproductive lives are believed to be driving some of the increase, said Dr. Ahmedin Jemal, a co-author of the report and senior vice president of surveillance and health equity science at the American Cancer Society.
More women are delaying childbearing, and they are having fewer children or no children at all. Many are not breastfeeding, which is believed protective. Earlier menstruation is a risk, as is late menopause.
All of these factors increase a woman’s exposure to the body’s estrogen and progesterone, hormones made by the ovaries that can stimulate cell growth.
Obesity, which has become more common among Americans, also raises the odds of breast cancer for postmenopausal women ages 50 and older. Being physically active and eating a healthy diet may help prevent the disease, experts say, while alcohol consumption and binge drinking increase the risk, accounting for more breast cancer cases than does obesity, Ms. Siegel said.
Far less is known about the role that environmental factors may play, including the effects of chemicals that mimic hormones, such as phthalates (used in many fragrances and personal care products), and that leach from food packaging.
Dani Alderman, 31, who lives in New York City, found out at age 27 that she had inherited a genetic mutation that raised her risk of breast and ovarian cancer. She started getting screened regularly, but doctors assured her that, even with her mutation, the risk was very small before age 30.
A week before her 30th birthday, however, a scan picked up something that turned out to be cancer.
“It’s really alarming,” Ms. Alderman said. “I have the gene, but something makes the gene express itself. I exercise five days a week, I don’t really drink alcohol, and I eat healthy. Is it the microplastics? The processed food? I think there must be something in the environment.”
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