ABSTRACT • Introduction : Breast cancer (BC) constitutes 38.6% of all female cancers in Lebanon, with yearly increasing incidence. HER2 overexpression is a strong predictive factor for sensitivity to HER2-targeted agents. This study aimed to report the prevalence of HER2-neu in newly diagnosed early or metastatic breast BC women in Lebanon and its pathological and clinical status.

Materials and Methods: This was a multicenter cross-sectiona study in women with histologically confirmed newly diagnosed early or metastatic BC from July 2010 till December 2012. All eligible women underwent immunohisto chemistry (IHC) test in local and reference laboratories. In-situ hybridization (ISH) testing was performed for discordant cases and HER2-neu IHC (2+) cases. Demographics and medical history were collected.

Results: 522 women were included (mean age at diagnosis : 54 ± 12 years). HER2-neu was positive in 190 (36.4%) women using ICH/ISH combined techniques. Overexpression of HER2-neu by the local laboratory was 21.8%. Concordance or correlation in IHC results between local and reference laboratories was significantly low (kappa = 0.27; p-value < 0.001). Positive HER2-neu status was significantly associated with estrogen-receptor-positive (p-value < 0.001), progesterone-receptor-positive (p-value = 0.04), presence of marker CA 15-3 (p-value = 0.03), and hormone replacement therapy (p-value = 0.04). Conclusion : The prevalence of HER2-neu positivity in newly diagnosed early or metastatic BC women is high in Lebanon. Identifying HER2-neu status is essential for managing BC as anti-HER2-neu therapy will be clinically beneficial for some patients but unnecessary for patients who are unlikely to respond.

Keywords: breast cancer; HER2-neu; immunohistochemistry (IHC); In-situ hybridization (ISH); overtreatment

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