In this exploratory analysis we use a combination of next-generation RNA sequencing, multiplex immunofluorescence (mIF) multispectral analysis for spatial composition evaluation, and immunohistochemistry (IHC) to characterize the tumor immune microenvironment of 108 pre-treatment primary tumor samples and 39 samples of metastases of 124 patients with HER2-positive MBC, including 15 paired samples. The gene discussed is ERBB2; the disease is neoplasm.