Hormone Receptor Positive/HER2 Negative Breast Carcinoma: Association of PIK3CA Mutational Status with PD-L1 and Tumor Cell Microenvironment and Their Prognostic Significance

Novel research data in different cancer types indicate that mutations within <i>PIK3CA</i> might serve as a biomarker of an improved response to immune therapy. Therefore, the aim of this study was to evaluate and examine possible differences in the tumor microenvironment composition and PD-L1 expression as well the prognostic significance of CD4, CD8, CD68, and CD163 in <i>PIK3CA</i> mutated and non-mutated hormone receptor positive and HER2 negative (HR+/HER2-) breast carcinoma. Breast carcinoma tissue was analyzed by Cobas <i>PIK3CA</i> mutation test for the presence of <i>PIK3CA</i> mutation and immunohistochemistry was applied to assess PD-L1 expression and CD4, CD8, CD68, and CD163 infiltration within tumor. Statistically significant association was observed between PD-L1 expression and the presence of <i>PIK3CA</i> exon 20 mutation (<i>p</i> = 0.044), with PD-L1-positive patients predominantly harboring this mutation. Tumors harboring <i>PIK3CA</i> mutations exhibited moderate to strong statistically significant positive correlations between PD-L1 expression and infiltration by CD8 cells (rs = 0.462, <i>p</i> = 0.0027), CD68 cells (rs = 0.398, <i>p</i> = 0.0134), and CD163 cells (rs = 0.617, <i>p</i> < 0.0001). In patients with <i>PIK3CA</i> mutation and exon 20 <i>PIK3CA</i> mutation there was statistically significant longer survival without recurrence (<i>p</i> = 0.026 and <i>p</i> = 0.041, respectively). Research regarding PD-L1 expression, immune cells and <i>PIK3CA</i> mutations might have an impact on how to determine therapeutic approaches for patients with HR+/HER2- breast carcinoma.