Survival outcomes of HER2 low patients with metastatic breast cancer: a retrospective analysis

Background: HER2 low (human epidermal growth factor receptor 2) expression is found in around 50–60% of breast cancer cases and is associated with poorer prognoses in early-stage breast cancer. This study evaluates survival outcomes in HER2 low metastatic breast cancer and compares them with other groups. Methods: This retrospective analysis examined metastatic breast cancer patients diagnosed between 2010 and 2023. HER2 low was defined as immunohistochemistry (IHC) 1+ or 2+ with negative fluorescence in situ hybridization (FISH). The primary objective was to compare overall survival between HER2 low and HER2 0 groups using Kaplan-Meier survival analysis with p-values to assess statistical significance. Results: A-hundred and twenty-eight patients with metastatic breast cancer were evaluated. Fifty-seven patients were luminal A (44.7%), 46 patients were luminal B (35.9%), and 25 patients (19.5%) were triple negative. Eighty-eight patients (68.8%) were HER2 0+, while 40 patients (31.2%) were in HER2 low (1+, 2+) group. In terms of genetic subtypes, metastatic status at diagnosis, age, The Eastern Cooperative Oncology Group (ECOG), both the HER2 0 and HER2 low groups showed the same results. Median survival of all patients was 28 months, while it was 40 months for luminal A group, 25 months for luminal B group, and 19 months for triple negative group. In the luminal A (p = 0.971), luminal B (p = 0.820) and triple negative groups (p = 0.444), survival rates of the HER2 0+ and HER2 low groups did not differ statistically significantly. Conclusions: In our study, no relationship was found between being in HER2 low group and poor survival in patients with metastatic breast cancer.

HER2 low; HER2 targeted therapies; Metastasis; Breast cancer; Triple negative; Overall survival

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