[1008] Serum HER2/nue extra-cellualar domain level predicts clinical response in the patients treated with sequential trastuzumab monotherapy and combination with chemotherapy.

Kashiwaba M, Inaba T, Wakabayashi G.. Iwate Medical University, Morioka, Japan

Background: Trastuzumab has >30% objective response rate in monotherapy and >70% in combination with chemotherapy in the patient with HER2/nue IHC 3+ or FISH+ at the first line therapy for metastatic breast cancer. Serum HER2/neu extracellular domain (HER2-ECD) is cleavage by the ADAM metalloproteinases. Previous trials suggested serum HER2-ECD level might be a predictive marker of clinical response. But the role of serum HER2-ECD level in serial treatments with trastuzumab and chemotherapy remains uncertain. Methods: Serial serum HER2-ECD levels ware measured at the point of initial day of treatment and evaluated day as treatment failure. Serum sampling was continued as long as trastuzumab was used. The new HER2/neu ELISA(Bayer Healthcare) was used to determine comparing with the results measured by ErbB-2 EIA(Nichirei). Results: Patients with >20% decrease in HER2-ECD level measured by HER2/neu ELISA had a significantly higher response rate and longer time to progression even in serial treatments. Conversely ErbB-2 EIA only showed good correlation with initial therapy but following HER2-ECD serum levels were not corresponded with clinical responses. Results: The HER2-ECD level is a significant predictive marker in the treatment with trastuzumab. This might select the patients who has higher response with trastuzumab or should be treated another therapy.

Thursday, December 14, 2006 5:00 PM

Poster Session I: Detection and Diagnosis: Circulating Markers (5:00 PM-7:00 PM)