Prognostic implications of HER2NEU‐low in metastatic breast cancer.

Introduction: We explored characteristics and clinical outcomes of HER2‐negative and HER2‐low metastatic breast cancers using real‐world data. Methods: We queried the National Cancer Database to identify MBC patients that were HER2‐low or HER2‐negative per immunohistochemical staining. A binomial regression analysis identified demographic and clinical correlates of each subtype. A Cox multivariable regression analysis (MVA) and propensity‐match analysis were performed to identify correlates of survival. Results: Excluding missing data, 24,636 MBC patients diagnosed between 2008 and 2015 were identified; 27.9% were HER2‐negative and 72.1% were HER2‐low. There were no relevant demographic differences between the groups. HER2‐low tumors were half as likely to have concomitant hormone receptor‐positive status (p < 0.01). The 3‐year survival rate among hormone receptor‐negative patients was 33.8% for HER2‐low and 32.2% for HER2‐negative (p < 0.05), and 60.9% and 55.6% in HER2‐low and HER2‐negative cases among hormone receptor‐positive patients (p < 0.05), respectively. HER2‐low cases were associated with better survival on MVA (HR =0.95, 95% CI 0.91–0.99) and remained superior with propensity‐matching (HR = 0.92, 95% CI 0.89–0.96). In a subset analysis isolated to hormone receptor‐positive cases, HER2‐low remained correlated with improved survival (HR = 0.93, 95% CI 0.89–0.98) with propensity‐matched MVA. Correlates of worse survival include older age as a continuous variable (HR = 1.02, 95% CI 1.02–1.02) and Black race (HR = 1.26, 95% CI 1.20–1.32) [all p < 0.01]. Conclusions: In the largest such analysis performed to date, our study demonstrates a small but statistically significant association with improved survival for HER2‐low tumors compared to HER2‐negative tumors in MBC. [ABSTRACT FROM AUTHOR]