Tumor Infiltrating Lymphocytes And Hydrophobic Amino Acid Changes In Her2-Positive Metastatic Breast Cancer.

592Background: In HER2-positive metastatic breast cancer (mBC), the role of tumor infiltrating lymphocytes (TILs) and mutation types remains unexplored. Herein we evaluated such parameters focusing on mutations changing chemical amino acid properties. Methods: Targeted NGS results were available for 136 primary tumors from an equal number of HER2-positive mBC patients, 96 of whom relapsed (R) following adjuvant treatment and 40 presented with metastatic disease (de novo). Coding mutations were analyzed for changed amino acid properties to hydrophobic, polar and charged. Outcome analyses (time to progression [TTP] and survival) were performed in trastuzumab-naive patients who received this drug upon diagnosis of mBC (N = 124). Results: A total of 1194 coding mutations in 58 genes were identified in 111/136 tumors (82%). Of these, 19% had a mean of 47 mutations and 22 mutated genes. R-mBC patients were richer in mutations as compared to de novo mBC (Kruskal-Wallis, p = 0.032). TILs density (mean: 14%; media...