Biomarkers of anti-angiogenic therapy in metastatic colorectal cancer (mCRC): original data and review of the literature.

INTRODUCTION: Tumour angiogenesis via vascular endothelial growth factor (VEGF) is essential for promoting tumour progression and is overexpressed in colorectal cancer. The humanised monoclonal anti-VEGF antibody bevacizumab (Avastin®, Genentech Inc., South San Francisco, CA) has shown activity in metastatic colorectal cancer (mCRC) combined with conventional chemotherapy. The search for biomarkers to predict response to anti-angiogenic therapy in mCRC is of great interest. We investigated several potential predictive anti-angiogenic markers including circulating endothelial progenitor cells (EPC) in patients with mCRC receiving bevacizumab containing treatment within a randomised multicenter phase 2 study of the German AIO GI tumour study group.

METHODS: We collected sequential blood samples and tumour tissues from patients participating in a clinical trial for patients with mCRC. We performed flow cytometry of mononuclear cells isolated from peripheral blood to assess CD 133 + or CD 34 + /KDR + EPC before the first bevacizumab containing chemotherapy and after 21 days. Circulating VEGF blood levels before a bevacizumab containing chemotherapy regimen and after 21 days and VEGF expression in tumour tissue were examined.

RESULTS: Patients with mCRC and a partial remission after six months of immuno-chemotherapy containing bevacizumab showed a reduction of CD 34 negative KDR positive cells as early as 3 weeks after start of therapy. In contrast, no remarkable change in the number of CD 34 /KDR positive or CD 34 /CD133 positive cells was seen. Furthermore, there was no correlation between treatment response and VEGF expression within the tumour tissue. The mAb bevacizumab reduced serum-VEGF levels in patients independent of their treatment response to bevacizumab.

DISCUSSION: We examined circulating endothelial progenitor cells (EPC), serum-VEGF levels and the tumour tissue VEGF expression of patients with mCRC under a bevacizumab containing chemotherapy. The patients with a partial remission after six months of immuno-chemotherapy showed a reduction of CD 34 negative KDR positive cells as early as 3 weeks after start of therapy. Neither serum nor tissue markers were of significant predictive value in our pilot study. Furthermore, we review the current data on biomarkers for anti-angiogenic therapy of mCRC.