Tumor-microenvironment Spatial Interaction to Identify Markers of Resistance to Therapy in HER2+ Breast Cancer Patients

This retrospective observational study aims at the comparison of the tumour-microenvironment tissue architecture before and after neo-adjuvant therapy in samples from HER2-positive (HER2+) breast cancer (BrCa) patients that display residual invasive disease in the breast/lymph node at surgery after standard-of-care combined chemotherapy and trastuzumab treatment. The working hypothesis of the investigators is that: Therapy imposes a selective pressure on tumour-microenvironment features promoting resistance to treatment. Participant that have already undergone neo-adjuvant treatment as part of their regular medical care for HER2-positive breast cancer will provide access to formalin-fixed paraffin-embedded (FFPE) samples taken before and after therapy. Tumoral, peri-tumoral and stromal regions of each specimen will be analyzed with the ultimate goal to identify new biomarkers (and putative targets) of resistance to therapy.