Investigating the Prognostic Relevance of Tumor Immune Microenvironment and Immune Gene Assembly in Breast Carcinoma Subtypes

SIMPLE SUMMARY: The tumor immune microenvironment of different breast carcinoma (BC) subtypes and immune gene assembly of metastasizing and non-metastasizing HER2-negative BCs was analyzed. Examination of 309 Hematoxylin and Eosin-stained slides highlighted that the distribution of tumor infiltrating lymphocytes (TILs) from peritumoral, stromal and intratumoral regions varied greatly within all subtypes, with most tumors (66.01%) belonging to the immunologically “cold” group. Hormone receptor (HR) negative subtypes generally showed higher immune activity in all analyzed regions. No survival benefit was detected based on the spatial distribution of TILs. A lower CD4(+)/CD8(+) ratio at the stromal internal tumor region indicated longer distant metastasis-free survival. When assessing immune gene expression between metastatic and non-metastatic BCs, the list of differentially expressed genes were non-identical across luminal and TNBCs, suggesting that these subtypes may use different mechanisms to bypass the immunological surveillance. Understanding these differences in the immune gene assembly may pave the way to the development of new immune-modulation therapies. ABSTRACT: We hypothesized that different BC subtypes are characterized by spatially distinct tumor immune microenvironment (TIME) and that immune gene assembly of metastatic (Met) and non-metastatic (Ctrl) BCs vary across subtypes. Peritumoral, stromal and intratumoral TIL was assessed on 309 BC cases. Hot, cold and immune-excluded groups were defined, and the prognostic role of this classification was assessed. CD4(+)/CD8(+) positivity was analyzed in 75 cases in four systematically predefined tumor regions. Immune gene expression of Met and Ctrl HER2-negative BCs was compared by using NanoString nCounter technology. The amount of TIL infiltration varied greatly within all BC subtypes. Two-third of the cases were cold tumors with no significant survival difference compared to hot tumors. A lower CD4(+)/CD8(+) ratio at the stromal internal tumor region was significantly associated with longer distant metastasis-free survival. The differentially expressed immune genes between Met and Ctrl varied across the studied BC subtypes with TNBC showing distinct features from the luminal subtypes. The TIME is characterized by a considerable heterogeneity; however, low level of TILs does not equate to disease progression. The differences in immune gene expression observed between Met and Ctrl breast carcinomas call attention to the important role of altered immune function in BC progression.