Rising Breast Cancer Incidence and Poor Outcomes in Young Women: A Retrospective Study.

Background and Aims: Recent studies suggest a rise in breast cancer (BC) among young women. We analyzed BC incidence patterns among women aged 18-40 in the TriNetX network from 2014 to 2023, stratifying by age, race, and ethnicity. We also examined mortality and local recurrence (LR) in women aged 18-40 diagnosed with primary BC. Methods: This retrospective study used data from the TriNetX network. Female patients aged 18-40 were identified, and the incidence proportion of primary BC from 2014 to 2023 was assessed using the TriNetX Incidence and Prevalence Analytics function, with stratification by age, ethnicity, and race. A second cohort of women aged 18-40 with a primary BC diagnosis was created to evaluate mortality and LR over the same period. All analyses were descriptive. Results: Among the 18,250,987 women aged 18-40 years in the TriNetX network, the incidence proportion of BC increased from 635 cases in 2014 to 4475 in 2023. White women accounted for the greatest number of BC cases; however, increasing incidence proportions were also observed among American Indian/Alaskan Native (AI/AN), Asian, and Native Hawaiian/Pacific Islanders (NHPIs) women over the last four years. Non-Hispanic women initially had higher incidence proportions but were surpassed by Hispanic women in 2022. Among 38,683 women aged 18-40 with primary BC, both mortality (0.09%-0.851%) and LR (0.3%-2.9%) increased over the study period. Conclusion: Within the TriNetX network, BC incidence proportion among women aged 18-40 demonstrated an upward trend from 2014 to 2023, particularly among non-Hispanic White women 30-39 years old. An uptrend was also seen in young AI/AN, Asian, NHPI, and Hispanic women. In addition, increased documented mortality and LR were also observed. These findings underscore the importance of further research to understand these trends and develop diagnostic and therapeutic approaches tailored to younger patients.