Baseline and recurrence levels of soluble HER2 (sHER2) in early-stage HER2-neu positive breast cancer (HER2+BC) from the NCCTG adjuvant Intergroup trial N9831

539 Background: An increased baseline sHER-2 concentration is an indicator of poor prognosis in the metastatic and adjuvant settings of HER-2+BC. This study evaluated the levels of sHER-2 during treatment and at time of recurrence in N9831. Methods: Aims were to describe sHER-2 levels during treatment and at time of recurrence in patients (pts) randomized to Arms A (standard chemotherapy) and C (standard chemotherapy with concurrent trastuzumab). Baseline serum samples of 1506 pts from both arms along with 86 recurrence serum samples were analyzed for sHER-2 (ng/mL). In addition, 556 serial samples were obtained in 148 patients over the treatment period. Median follow up was 4.5 years. Statistical methods included repeated measures linear models, Wilcoxon rank sum tests, and Cox regression models. Results: Analyzing serial sHER-2 levels during treatment, mean log sHER-2 remained constant in Arm C (estimated slope = 0.004, p = 0.44) while the estimated increase per month was 0.026 (on log e scale) for Arm ...