Occurrence and outcome of de novo metastatic breast cancer by subtype in a large, diverse population

Purpose To examine the occurrence and outcomes of de novo metastatic (Stage IV) breast cancer, particularly with respect to tumor HER2 expression. Methods We studied all 6,268 de novo metastatic breast cancer cases diagnosed from 1 January 2005 to 31 December 2011 and reported to the California Cancer Registry. Molecular subtypes were classified according to HER2 and hormone receptor (HR, including estrogen and/or progesterone receptor) expression. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95 % confidence intervals (CIs) of Stage IV versus Stage I-III breast cancer; Cox proportional hazards regression was used to assess relative hazard (RH) of mortality. Results Five percent of invasive breast cancer was metastatic at diagnosis. Compared to patients with earlier stage disease, patients with de novo metastatic disease were significantly more likely to have HER2? tumors (HR+/HER2+: OR 1.29, 95 % CI 1.17-1.42; HR-/HER2+: OR 1.40, 95 % CI 1.25-1.57, vs. HR+/HER2-). Median survival improved over time, but varied substantially across race/ethnicity (Asians: 34 months; African Americans: 6 months), neighborhood socioeconomic status (SES) (highest: 34 months, lowest: 20 months), and molecular subtype (HR+/HER2+: 45 months; triple negative: 12 months). In a multivariable model, triple negative (RH 2.85, 95 % CI 2.50-3.24) and HR-/HER2+ (RH 1.60, 95 % CI 1.37-1.87) had worse, while HR+/HER2+ had similar, risk of all-cause death compared to HR+/HER2-breast cancer. Conclusions De novo metastatic breast cancer was more likely to be HER2+. Among metastatic tumors, those that were HER2+ had better survival than other subtypes.