Breast cancer remains one of the most significant health challenges worldwide, with approximately 5% to 10% of patients diagnosed at a metastatic stage. Among these, a subset presents with human epidermal growth factor receptor 2 (HER2)-positive de novo metastatic breast cancer (dnMBC), a category that has been poorly characterized until now.
Study Overview
Researchers at the National Cancer Institute in Mexico City conducted a retrospective cohort study analyzing a decade of patient data from 2010 to 2020. The study included 145 women with HER2-positive dnMBC, examining sociodemographic factors, clinical and pathological features, treatment patterns, and receptor status. Survival outcomes, including overall survival (OS) and progression-free survival (PFS), were also evaluated.
Patient and Clinical Characteristics
Among the patients, 40.7% were HER2+ ER+ PR+, 40% were HER2+ ER- PR-, 13.1% were HER2+ ER+ PR-, and 6.2% were HER2+ ER- PR+. At the time of analysis, 33.8% of patients were alive, 29% had died, and 37.2% were lost to follow-up. Median follow-up was 42 months, ranging from 27 days to 166 months.
Patients had a median age of 52 years, with the majority (94.5%) lacking health insurance and 77.2% identified as housewives. Geographically, most patients (85.5%) originated from central Mexico. Educational levels varied, with 37.2% having completed elementary school and only 10.3% holding a bachelor’s degree.
Tumor and Pathological Findings
Invasive ductal carcinoma was the most common histological type (85.5%). Tumors showed a high burden of disease: 62.1% were classified as T4, and 64.1% had N3 lymph node involvement. Metastatic sites varied, with 46.9% of patients presenting with a single metastasis, and 51.7% showing visceral metastases at diagnosis. Pathological analysis highlighted the presence of inflammatory cells in 82.1% of tumors, lymphovascular invasion in 46.2%, and high Ki67 expression (>45%) in 43.4% of patients.
Treatment Patterns
Palliative mastectomy was performed in 15.2% of patients. Radiotherapy was administered primarily to the breast (60%), followed by the brain (35.2%) and vertebral column (15.9%). All patients received at least one line of treatment, with some undergoing up to 10 lines. Treatment patterns varied slightly according to hormonal receptor status.
Survival Outcomes
The median overall survival (OS) for all patients was 96 months, with a median progression-free survival (PFS) of 18.7 months. Survival rates were 94% at one year, 84% at two years, 77% at three years, 73% at four years, and 66% at five years. No statistically significant differences in OS or PFS were found between hormonal receptor subgroups. Multivariate Cox regression analysis did not identify social or demographic factors significantly associated with survival outcomes.
Key Insights
This study offers valuable descriptive insights into HER2-positive dnMBC in the Mexican population, highlighting high tumor burden at diagnosis, diverse receptor expression, and prolonged survival compared to previous reports. While no statistically significant differences were observed across hormonal receptor groups, the findings suggest that treatment patterns, including targeted HER2 therapy, may contribute to improved outcomes.
Researchers noted that social variables such as marital status, education, occupation, insurance, and geographic origin did not significantly influence survival, emphasizing the role of tumor biology in determining outcomes. Despite limitations, including high lost-to-follow-up rates and the retrospective design, this study provides a foundational dataset for future clinical trials and treatment strategy optimization.
Conclusion
HER2-positive de novo metastatic breast cancer presents unique clinical and pathological characteristics. This 10-year study reinforces the importance of comprehensive treatment strategies and provides baseline data for further research into survival determinants and therapeutic approaches. Continued investigation is needed to clarify the impact of hormonal receptor status and social factors on long-term outcomes.
