De novo metastatic Her2+breast cancer in a diverse population of women under age 40

e13045 Background: Breast cancer (BC) is the most common malignancy among women. Her2 mutation has historically been associated with more aggressive disease and worse prognosis, however this paradigm is changing with Her2-directed therapies. Her2 positive BC presents with de novo metastatic disease more often than other subtypes. Young women are more likely to be diagnosed with Her2 positive BC, however previous studies have not had adequate representation of Black/African American women. We evaluated a diverse group of young women under the age of 40 to determine if Her2+ disease was more likely to present with de novo metastatic disease. Methods: We performed a retrospective chart review and collected data on 746 women diagnosed with BC under the age of 40 from 2012 to 2022. We collected age at diagnosis, Her2 receptor status, self-identified race, and stage at diagnosis. 187 of these patients were Her2 positive, and 276 patients were Black. We stratified patients as Black versus White, and as stage IV at diagnosis versus stages I to III at diagnosis. We performed Fisher's exact test to determine if Her2 positive BC was more or less likely to present as de novo metastatic disease compared to Her2 negative BC. Results: In our population of 746 young women under the age of 40 presenting to our health system in a 10-year period, 48 (6.4%) presented with de novo metastatic BC, and 19 (39.6%) of these were Her2 positive. 36% of our study population was Black, which is representative of the demographics of our region. We performed Fisher's exact test, and found that Her2 positive BC was more likely to present as de novo metastatic disease compared to Her2 negative BC. This was statistically significant (p = 0.024). When divided for race, this was not statistically significant for White patients alone (p = 0.052) or Black patients alone (p = 0.234). Conclusions: Our data shows that Her2 positive BC in women under the age of 40 is statistically more likely to present with de novo metastatic disease. Previous research in this area has not been inclusive of Black patients. Current guidelines only recommend staging imaging among patients with systemic symptoms. Based on this data, consideration should be made for staging scans for young women presenting with new HER2+ breast cancer diagnoses. There is limited data available for breast cancer subtype incidence and prognosis among Black patients, and this study underscores the need for more inclusive study populations.[Table: see text]