Fig 2: CD44 is induced shortly after HER2 inhibition in breast cancer tumor cells (A–D). The bar charts illustrate the expression of CD24 and CD44 in BT-474 (A) and SKBR3 (B) measured by flow cytometry at 1, 4, and 24 h after treatment with 0.75 µM of lapatinib. (C). Histograms of CD44 expression after treatment. (D). Cell viability was assessed using an MTT assay in BT-474 and SK-BR-3 cells. Data were normalized to the control (vehicle). Data are the mean ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001. T0: 4 days after lapatinib treatment; T14: 14 days after drug removal; DMSO: dimethyl sulfoxide (vehicle control for lapatinib).

Fig 3: HER2 inhibition induces CD44 in dormant breast cancer tumor cells. (A–L). The bar charts illustrate the expression of CD24 and CD44 in BT-474 (A–F) and SK-BR-3 (G–L) measured by flow cytometry at T0 (A–C,G–I) and T14 (D–F,J–L) using lapatinib concentrations of 0.1875, 0.375, and 0.75 µM. Data were normalized to the control (vehicle). Data are the mean ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. T0: 4 days after lapatinib treatment; T14: 14 days after drug removal; DMSO: dimethyl sulfoxide (vehicle control for lapatinib).

Fig 4: JAK1 inhibition impairs proliferation in the CD24+/CD44+ subpopulation during recovery after HER2 inhibition. (A–F). The bar charts illustrate the expression of CD24 and CD44 in Ki67-positive SK-BR-3-Cas9 cells expressing sgJAK1 or sgSTAT3 after treatment with 0.375 and 0.75 µM of lapatinib at T0 (A–C) and T14 (D–F). (G,H). Treatment effect on cell viability using an MTT assay. Data are the mean ± SD. ** p < 0.01, ns = not significant. T0: 4 days after lapatinib treatment; T14: 14 days after lapatinib removal; DMSO: dimethyl sulfoxide (vehicle control for lapatinib).

Fig 5: CD44-expressing tumor cells exhibit sustained proliferative potential following HER2 inhibition. (A–D). The bar charts illustrate the expression of CD24 and CD44 in Ki67-positive BT-474 (A,C) and SK-BR-3 (B,D) subpopulations measured by flow cytometry at T0 and T14 after treatment with 0.375 and 0.75 µM of lapatinib. Data are the mean ± SD. * p < 0.05, ** p < 0.01. T0: 4 days after lapatinib treatment; T14: 14 days after drug removal; DMSO: dimethyl sulfoxide (vehicle control for lapatinib).