In line with this hypothesis, quantitative real-time reverse transcription PCR (qRT-PCR) analysis of the 61 HER2+ breast cancer biopsies showed that DPAGT1 mRNA expression was significantly upregulated in trastuzumab-resistant tissues compared with sensitive tissues and was significantly associated with the serum HER2-ECD level (R2 = 0.3306, P < 0.001) in these patients (Figure 1, G and H). Here, ERBB2 is linked to breast cancer.