EGFR and neoplasm: We also observed that activated EGFR (pY845) was specifically co-localized with CD44 in clustered MDA-MB-231 TNBC tumor cells in suspension, mimicking a suspension condition of CTCs, but not in the adherent cells (Figure 2E, Figure S2E), suggesting a specific synergistic interaction between activated EGFR and CD44 during CTC clustering.