The rate of late-stage breast cancer diagnoses in young women also has been climbing. In women under age 40, the rate has increased by about 3 percent each year from 2000 to 2019, according to data from the American Cancer Society.
And while breast cancer mortality rates for older women declined from 2010 to 2017, the rate among younger women did not decrease.
Experts say there are no clear explanations why more women are being diagnosed with breast cancer at younger ages, but there are several possible factors.
Genetics is a known risk factor for breast cancer, but that does not appear to be driving the trend, said Elizabeth Suh-Burgmann, chair for gynecologic oncology for Kaiser Permanente’s Northern California region. Most women who develop breast cancer at a young age don’t have a genetic risk, she said.
One possible contributing factor, Suh-Burgmann said, is that more women are delaying their first pregnancy. Getting pregnant for the first time at age 35 or later is a risk factor for breast cancer. One theory is that after the age of 35, breasts have had more time to accumulate abnormal cells. Changes in the breast that occur during pregnancy can accelerate the development of those abnormal cells into cancer, Suh-Burgmann said.
