CD63 and breast cancer: Expression of CD63 in formalin-fixed, paraffin-embedded (FFPE) BC cell-line pellets also supported this observation (Figures 1J, K), with HER2+ breast cancer cell lines demonstrating significantly higher levels of CD63 staining (confined often to discrete intracellular structures) than non-HER2+ (MDA-231 and MCF7) cell-line pellets (Figure 1K).