DETECT III: A multicenter, randomized, phase III study to compare standard therapy alone versus standard therapy plus lapatinib in patients (pts) with initially HER2-negative metastatic breast cancer but with HER2-positive circulating tumor cells (CTC).

TPS1146 Background: HER2 status may change over the course of disease in breast cancer pts. Approx. 20-30% of pts with initially HER2-negative breast cancer have HER2-positive metastasis (Zidan et al. 2005; Tewes et al. 2009). Determining HER2 status on CTC is one option to re-evaluate HER2 status at the time metastasis is diagnosed. Currently it is unclear if HER2-targeted therapy based on the assessment of HER2 status of CTC reveals a clinical benefit. Methods: This is a randomized, open-label, two arm phase III study to investigate the clinical efficacy of lapatinib, as a HER2-targeted therapy in initially HER2-negative metastatic breast cancer pts with HER2-positive CTC at the time of distant disease. As only half of the pts with HER2-negative metastatic breast cancer show CTC-positivity and of those approx. 32% will exhibit HER2-positive CTC (Fehm et al. 2010), screening of about 1420 pts is required to enroll 228 pts. Main inclusion criteria: metastatic breast cancer with HER2-negative primary tumor tissue and/or biopsies from metastatic sites or locoregional recurrences, evidence of ≥1 HER2-positive CTC and ≥1 measurable metastatic lesion according to RECIST. Eligible pts will be randomized 1:1 to receive standard treatment vs. standard treatment plus lapatinib. Standard chemo- or endocrine therapy must be approved in combination with lapatinib or been investigated in prior clinical trials. Primary endpoint is progression free survival. Secondary endpoints include overall response rate, clinical benefit rate, overall survival and dynamic of CTC. The DETECT III trial is one of the first trials where treatment is based on phenotypic characteristics of CTC. If this trial succeeds in proving efficacy of lapatinib in pts with initially HER2-negative metastatic breast cancer but HER2-positive CTC, this will establish a new strategy in the treatment of metastatic breast cancer.