The increase in breast cancer rates among younger patients is occurring as the incidence of other early-onset cancers — including colorectal, gastric, kidney and liver cancer — is also on the rise, though cancer among patients under 50 is still relatively rare overall, Dr. Partridge said.

Women are now being diagnosed with cancer more often than men in certain age groups, according to a new report from the American Cancer Society. Among adults aged 50-64, cancer rates are slightly higher in women, and women under 50 are almost twice as likely as men in the same age group to receive a cancer diagnosis.