TUESDAY, Jan. 30, 2024 (HealthDay News) — There has been an increase in breast cancer incidence rates among young U.S. women from 2000 to 2019, according to a study published online Jan. 26 in JAMA Network Open.

Shuai Xu, M.P.H., from Washington University School of Medicine in St. Louis, and colleagues assessed recent trends and how period and cohort effects may affect trends in breast cancer incidence among young U.S. women (aged 20 to 49 years). The analysis included data from 217,815 women with a primary invasive breast cancer identified from the Surveillance, Epidemiology, and End Results registries (2000 to 2019).

The researchers found that the majority were diagnosed with an estrogen receptor (ER)-positive/progesterone receptor (PR)-positive tumor (61.5 percent) and were diagnosed with a stage I tumor (37.6 percent). There was an overall increase in incidence of invasive breast cancer (average annual percent changes [AAPC], 0.79), with similar trends seen across almost all racial and ethnic groups. Age-standardized incidence rates (ASIR) increased for ER-positive/PR-positive (AAPC, 2.72) and ER-positive/PR-negative tumors (AAPC, 1.43), but decreased for ER-negative/PR-positive tumors (AAPC, −3.25). ASIR were highest among non-Hispanic Black women (aged 20 to 29 years: incidence rate ratios [IRR], 1.53; aged 30 to 39 years: IRR, 1.15). However, for women aged 40 to 49 years, ASIR was lower for non-Hispanic Black women versus non-Hispanic White women (IRR, 0.96). Both cohort and period effects were seen on breast cancer incidence in an age-period-cohort analysis.

“These results suggest that understanding factors driving differential trends in incidence rates for different age groups by race and ER-positive status should provide insights into breast cancer prevention in young women,” the authors write.

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