ERBB2 and breast cancer: Using different breast cancer cell lines reflecting the different subtypes of breast cancer with distinct expression levels of HER2 that allowed us to stain EVs released from cancer cells for their expression of HER2: BT474 cells (HR+HER2+, resembling luminal B-like breast cancer), MCF-7 (HR+HER2neg; resembling luminal A breast cancer), SKBR-3 cells (HRnegHER2+; HER2-enriched breast cancer) and MDA-MB-231 cells (HRnegHER2neg; derived from a triple-negative breast cancer).