Immunomorphological specifcity of HER2-low breast cancer

Assessment of tumor infltrating lymphocytes (TiLs) has been recognized as an additional tool for predicting survival in triple negative (TN) and HER2/neu positive (HER2+) subtypes of breast cancer (BC). Recently, BC, including the above-mentioned subtypes and characterized by low/undefined expression of HER2/neu, has been isolated into a separate group, designated HER2-low BC. The relationship between clinical and morphological parameters of HER2-low breast cancer and infiltration by immunocompetent cells, including tumor associated macrophages (TAM), has not been studied to date. The purpose of the study was to identify significant relationships between the level of subpopulations of immunocompetent cells (Tils + TAM) and the clinical and morphological parameters of HER2-low BC. Material and Methods . The study examined the surgical specimens of 33 patients with HER2-low BC. Visual counting of TILs and assessment (IHC) of the level of T-helpers, T-killers, M1 and M2 macrophages were carried out in intratumor sites and the invasive edge of the primary tumor. Results . The study of mastectomy specimens showed that infiltration of Tils (Me=5 [5; 10] %) was observed in all 33 patients. The level of M2 of macrophages was found to be the highest both in the invasive margin and in the intratumor sites (CD163inv: Me=20 [10; 40] %; CD163c: Me=15 [7; 30] %, respectively). In patients with high (≥20 %) levels of M2 macrophages in the invasive margin, there was also a high level of other immunocompetent cells, and perineural invasion was detected significantly more often (р=0.019). Conclusion . A high level of infiltration by M2 macrophages of the invasive margin is combined with the detection of perineural invasion in primary HER2-low breast cancer, which is one of the predictors of a high risk of progression. In combination with other clinical and morphological parameters, the level of M2 macrophages in HER2-low breast cancer may become another factor in predicting disease prognosis.