Factors Associated With Short- and Long-Term Survival in Metastatic HER2-Positive Breast Cancer.

Background: We sought to evaluate prognostic factors in human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) and their relationship with short- and long-term overall survival (OS).

Methods: Using the Surveillance, Epidemiology, and End Results (SEER) database, we evaluated patients with de novo HER2-positive MBC diagnosed from 2010 to 2018. Univariate analyses were performed to determine effect of each variable on OS. Significant variables were included in a multivariate Cox model for OS. Univariate and multivariate logistic regression were used to evaluate the association of each variable with short- (<2 years) and long- (≥5 years) term OS.

Results: Overall, 5576 patients were included. Median follow up was 48 months (interquartile range 25-73 months), and median OS was 41 months. The proportion alive at 2, 5, and 8 years was 63.3% (95% confidence interval [CI] 62.0%-64.7%), 37.8% (95% CI, 36.2%-39.4%), and 26.8% (95% CI, 24.8%-28.9%), respectively. Factors associated with short-term OS were older age; Black race; nonductal nonlobular; brain, liver, or lung metastases; estrogen/progesterone receptor (ER/PR)-negative disease, and lower income (all P < .04). Number of metastatic organ sites was not significant. Factors associated with long-term OS were younger age, White race, fewer metastatic organ sites, ER/PR-positive disease, and higher income (all P < .02). Specific organ sites were not significant.

Conclusions: In this cohort with de novo HER2-positive MBC, OS improved significantly over the study period. We identified patient-specific and tumor-specific factors that were associated with short- and long-term survival in HER2-positive MBC.