Breast cancer is the second most common cause of cancer death in women in the United States and accounts for 30% of all cancers in women.

For the last three decades, breast cancer survival rates have been improving significantly for women in each age decade from 20 to 79 years, but a new study shows the trend has flattened for women under 40. 

The study, which retrospectively analyzed data from the National Center for Health Statistics from 1969 to 2017, shows breast cancer mortality rates stopped declining after 2010 for women aged 20 to 39 years.

Conversely, researchers found that the downward trend has continued for women aged 40 to 79 years.

The change is most likely due to a significant increase in late-stage breast cancer for women younger than age 40. According to the study, the distant-stage breast cancer, meaning cancer that has spread to distant parts of the body, rate in women aged 25 to 39 years was 3.84 per 100,000 women in 2015—a 151% increase since 1976 and a 32% increase since 2009.

“Younger women are more likely to have triple-negative breast cancers and human epidermal growth factor receptor 2–positive disease; both are more aggressive subtypes,” the researchers wrote.

“At Moffitt Cancer Center, we recommend that each woman age 40 and over get a mammogram of both breasts every year, as long as the woman remains in good health,” said Dr. Bethany Niell, section chief of Breast Imaging at Moffitt.

Niell added that all women should discuss their breast cancer risk factors with their doctor before the age of 30. “Women with an increased risk of developing breast cancer may need to begin screening as early as age 25,” said Niell. “Some high risk women may benefit from screening with mammography and breast MRI every year.”   

Regardless of age, if a woman feels a new lump, she should talk with her doctor. “New lumps, including in younger women, often require further evaluation with an ultrasound or mammogram,” said Niell.