Plasma HER2ECD a promising test for patient prognosis and prediction of response in HER2 positive breast cancer: results of a randomized study - SAKK 22/99

The HER2 extracellular domain shed in blood (HER2 ) is reported to rise and fall in parallel with HER2+ breast cancer behavior. In this study, we evaluated the clinical relevance of plasma HER2 values in patients with metastatic breast cancer treated in the SAKK22/99 trial comparing trastuzumab monotherapy followed by trastuzumab-chemotherapy combination at progression versus upfront combination therapy. Quantitative assessment of plasma HER2 was performed in 133 patients at baseline; after 2-24 h; at 3 weeks; at first response evaluation (8-9 weeks); and at tumor progression. Associations with tumor characteristics, disease course and trial treatment were evaluated. Baseline HER2 levels were stable within 24 h after the first trastuzumab injection. These plasma values correlated positively with the HER2 gene ratio (r = 0.39, P