Monitoring of Trastuzumab-mediated ADCC activity in HER2-positive patients according to the FcγRIIIa polymorphism. Representative data obtained against the HER2-overexpressing cell line MDA-MB-453 using patients’ PBMCs collected at diagnosis, and at the 12° and 24° weeks (W) of NC treatment. A. Data were classified by the V/V (n = 9), V/F (n = 17), and F/F (n = 10) genotypes of the FcγRIIIa polymorphism. Statistical analysis was performed with the Kruskal-Wallis test. B. Analysis was performed comparing V carriers (n = 26) with F/F individuals, through the Wilcoxon test. Graphs on the left show the absolute percentage of lysis measured at a 30:1 Effector:Target ratio. Natural Killer (NK) cells were identified in flow cytometry as CD3-CD16 + CD56dim lymphocytes. Histogram plots on the right display normalized lysis calculated for 10,000 NK cells. Data are represented as means and standard deviations. The Student t test was employed for NK cells percentage variations. *Chi-square or |Z| < 0.05. **P < 0.05. HER2, human epidermal growth factor receptor-2.