HER-3 molecular classification, expression of PD-L1 and clinical importance in breast cancer

Receptors of the large HER family play an important role in breast cancer, which is undergoing a gradual development in connection with biological development, both in the field of diagnostics and therapy. Dimerization of HER-2 with other HER members, such as HER-3, is the biggest driver of tumor cell growth and survival. Numerous studies show that HER-3 gene overexpression correlates with poor prognosis. However, other studies have shown HER-3 overexpression to be a positive prognostic factor. HER-3 may confer resistance to certain EGFR or HER-2 receptor therapeutics. An interesting fact, however, is that HER-3 expression can serve as a marker in immunotherapy for triple-negative breast cancer (TNBC). It is thought to be involved not only in cell survival and proliferation, but also in the regulation of PD-L1 expression. In breast cancer, PD-L1 expression is heterogeneous and is generally associated with the presence of tumor‑infiltrating lymphocytes and a number of factors with poor prognosis such as young age, hormone receptor negativity, and high HER-2 expression and proliferation index. Our results showed amplification of HER-3 (CERB3) in 2 out of a sample of 20 patients with TNBC, and 13 of 20 HER-2‑positive patients. PD-L1 expression was demonstrated in 3 out of 13 HER-3‑positive patients and 2 out of 2 HER-3‑positive TNBC patients. There was a strong correlation between positive HER-3 and PD-L1 TNBC expression (p = Keywords: breast cancer, HER family, overexpression, HER-3, HER-2, PD-L1, TNBC.