Parity and Breast Cancer US 1935-2015

Trends in Parity and Breast Cancer Incidence in US Women Younger Than 40 Years From 1935 to 2015

Sarah M. Lima, MPH¹; Rebecca D. Kehm, PhD¹; Katrina Swett, MS²; et alLou Gonsalves, PhD²; Mary Beth Terry, PhD^1,3

Author Affiliations Article Information

JAMA Netw Open. 2020;3(3):e200929. doi:10.1001/jamanetworkopen.2020.0929

Key Points Español  中文 (Chinese)

Question  Can the increase in breast cancer incidence in US women aged 25 to 39 years be explained by trends of decreasing parity?

Findings  In this population-based cohort study including Connecticut women aged 25 to 39 from 1935 to 2015, breast cancer incidence statistically significantly increased by 0.65% per year; after considering parity trends, the annual increase was of similar magnitude and therefore could not explain the trends in breast cancer.

Meaning  These findings suggest that secular trends in parity cannot explain the increasing incidence rate of breast cancer in young women, and this increase cannot be primarily attributed to mammography screening, as the trend analysis shows the increase started prior to screening.