Immunohistochemical expression of epidermal growth factor receptor: prognostic value in HER2 positive breast cancer.

Introduction: Epidermal Growth Factor Receptor (EGFR) expression is not well-studied in Human Epidermal Growth Factor Receptor 2 (HER2) positive breast cancer. We aim to study the prevalence of EGFR immunohistochemical expression in HER2-positive breast carcinomas and to correlate this expression with different anatomo-clinical parameters.

Methods: It was a retrospective study involving cases of HER2-positive breast carcinoma collected at the Immuno-Histo-Cytology Department of Salah Azaïez Institute of Tunis between 2018 and 2020. An immunohistochemical study using the anti-human EGFR monoclonal antibody was performed. Cases with an overall score ≥1+ were considered positive.

Results: Fifty patients were included. EGFR expression in HER2-positive breast carcinomas was more likely to occur in patients under the age of 50 (p = 0.063). It was significantly associated with the absence of lymphovascular invasion (p = 0.047). In multivariate analysis, young age, absence of lympho-vascular invasion, and high Ki67 proliferation index (>60%) were independently associated with positive EGFR expression (p = 0.047, p = 0.040, and p = 0.050, respectively).

Conclusion: Through this first Tunisian study, our data revealed that the immunohistochemical expression of EGFR is associated with young age, absence of lymphovascular invasion, and a high mitotic index (Ki67), which may suggest a potential predictive value for chemotherapy response.