Furthermore, in SBC-3/ETP xenografts, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining showed that trastuzumab significantly induced apoptosis of SCLC cells (apoptosis index was 6.20 ± 1.63% in trastuzumab group vs. 2.10 ± 0.97% in control group, P = 0.003), despite the downregulation of cell surface HER2 expression upon trastuzumab treatment (Figure 3b and c). Here, ERBB2 is linked to small cell lung carcinoma.