Changes over time of extracellular domain of HER2 (ECD/HER2) serum levels have prognostic value in metastatic breast cancer

Background Blood levels of the extracellular domain of HER-2/neu (ECD/HER2) have been suggested to have potential as a tumor marker in breast cancer. Our aim was to assess the prognostic value of baseline levels of ECD/HER2, but more importantly changes in levels over time, in women with metastatic breast cancer. Methods Baseline and serial levels of ECD/HER2 were measured in 158 women with newly-diagnosed metastatic breast cancer, in whom we previously performed serial measurement of plasma osteopontin. ECD/HER2 was measured in 1,282 serum samples using a validated ELISA at baseline and every 3-12 weeks during and after therapy until death (median, n = 8 samples per patient). Multivariate time-dependent survival analyses were conducted using models that right-censored patient outcomes 3, 6 and 12 months after last known ECD/HER2 measurement. Results Thirty-four patients (22%) had elevated baseline ECD/HER2 (median 10.2 ng/ml: range 4.1-40.4 ng/ml). In univariate analysis, elevated baseline ECD/HER2 was associated with short survival (P = 0.001). In a multivariate model incorporating standard clinical prognostic factors, baseline ECD/HER2 was significantly associated with survival duration (RR 1.029; P = 0.020). Presence of visceral metastases and ECOG status 2-4 also retained significance. In a multivariate model incorporating standard prognostic factors and changes in sequential ECD/HER2 levels, an ECD/HER2 increase of > 12 ng/ml at any time was the variable with most prognostic value for poor survival (RR 6.10; P = 0.0003); poor ECOG status also retained significance. Conclusion Increases over time of ECD/HER2 levels were strongly associated with poor survival in this cohort of women with metastatic breast cancer.