Characteristics of Patients with De Novo Metastatic Breast Cancer and Positive Human Epidermal Growth Factor Receptor 2 in a Reference Center in Mexico

Background Breast cancer is an important disease with a high burden worldwide; approximately 5% to 10% of cases are diagnosed as metastatic breast cancer. A subset of patients with human epidermal growth factor receptor 2 (HER2) positivity and stage IV disease at diagnosis are identified as having HER2-positive de novo metastatic breast cancer, which is poorly characterized. Methods A retrospective cohort study was performed at the National Cancer Institute in Mexico City using 10 years of collected data. Variables included patient status, sociodemographics, and clinical, pathological, treatment patterns, and receptor status, while overall survival (OS) and progression-free survival (PFS) were also estimated. For assessing possible differences between receptor-status groups, a Fisher's exact test was performed. Survival analyses were performed using Kaplan-Meier plots, and a log-rank test was used to evaluate possible differences. Multivariate survival analyses for social and demographic variables were performed using Cox's proportional hazard model. Results A total of 145 patients were identified, and out of them, 40.7% were classified as HER2+ ER+ PR+, 40% as HER2+ ER- PR-, 13.1% as HER2+ ER+ PR-, and 6.2% as HER2+ ER- PR+. The median OS of all patients was 96 months (95% confidence interval (CI): 79 to not estimable) and PFS was 18.7 months (95% CI: 14.5-27.3). Survival rates for all patients were 94%, 84%, 77%, 73%, and 66% for years one through five, respectively. Only few statistical differences were found in descriptive analysis; in the log-rank test and Cox's proportional hazard model, no differences or associations were found. Conclusions Breast cancer is a leading cause of mortality and morbidity worldwide with several different outcomes depending on the clinical stage and molecular profile. Recently, de novo metastatic breast cancer has been studied because of positive outcomes after treatment, and several therapeutic strategies have been employed to increase patients' survival rate. This study provided descriptive results of clinical, sociodemographic, treatment patterns, and pathological characteristics in HER2-positive de novo metastatic breast cancer in patients according to molecular receptor status. No relevant statistical significance was found; the exploratory survival outcomes should be interpreted as exploratory due to high lost-to-follow up rate. These results could be useful in terms of design of future clinical trials.