Abstract B03: The predictive value of microvessel density, vascular proliferation index and markers of VEGF associated angiogenesis in patients with metastatic melanoma treated with bevacizumab monotherapy

Abstract

Abstract Background: Angiogenesis is a hallmark of cancer and essential for tumor growth and metastases. As previously published, clinical benefit was observed in 31% of patients with metastatic melanoma who were treated with bevacizumab monotherapy. Response evaluation was done according to the RECIST guidelines; overall response (OR) defines patients with complete or partial response, clinical benefit (CB) includes also stable disease for at least 6 months. The main objective of this study was to identify predictive markers of anti-angiogenic treatment. Here, we focus on the correlation between microvessel density and treatment response. Methods: 35 patients were enrolled in an open-label single arm phase II clinical trial at Haukeland University Hospital, Norway, and were treated with bevacizumab 10mg/kg q14 until disease progression or intolerable toxicity (ClinicalTrials.gov: NCT00139360). Paraffin embedded tissue of primary tumors and metastases as well as blood samples were available for investigation. Tissue sections were double stained with antibodies for Factor VIII and Ki67. The sections were screened for areas with the highest density of Factor VIII positive vessels. For assessment of microvessel density (MVD), the number of Factor VIII positive vascular units within the tumor was registered in three high power fields (HPFs). Microvessels with co-expression of Ki67 in the nucleus and Factor VIII in the cytoplasm of endothelial cells (ECs) were defined as proliferating vessels (pMVD) and were counted in the same HPFs. The ratio between pMVD and MVD was defined as vascular proliferation index (VPI). In addition, the presence of glomeroid microvascular proliferations (GMPs) was registered in tissue sections stained with Factor VIII mono. GMPs, a marker for VEGF associated angiogenesis, were defined as focal glomerulus-like aggregates of multi-layered Factor VIII positive ECs with a minimum of 15 cells. Associations with response as well as with various angiogenic factors in tissue and blood samples were analyzed. Results: High pMVD and VPI were significantly associated with high expression of vascular endothelial growth factor A (VEGF-A) in primary melanomas (Mann-Whitney U test, p=0.023; p=0.032). In addition, high MVD in metastases was associated with high expression of VEGF-A in metastases and low VEGF-A concentration in plasma (Mann-Whitney U test, p=0.036; p=0.046). However, expression of VEGF-A in primary melanomas or metastases was not associated with treatment response. All primary melanomas with GMPs show expression of VEGF-A in ECs (Chi-square test p=0.029). High MVD in primary tumors predicted CB (Mann-Whitney U test, p=0.042). However, this correlation was not observed in the metastases. Still, neither MVD in primary melanomas nor in metastases was correlated with OR to bevacizumab monotherapy in patients with metastatic melanoma. VPI and pMVD in primary melanomas or metastases were not correlated to any kind of treatment response. Similarly, the presence of GMP in primary melanomas or metastases did not show any correlation to treatment response. Conclusion: Although a significant association was present between MVD in primary lesions and CB, neither MVD, pMVD or VEGF expression seems to be robust predictive markers of response to bevacizumab monotherapy for metastatic melanoma. Further investigation is ongoing to identify predictive biomarkers in this trial. Citation Format: Cornelia Schuster, Lars A. Akslen, Oddbjørn Straume. The predictive value of microvessel density, vascular proliferation index and markers of VEGF associated angiogenesis in patients with metastatic melanoma treated with bevacizumab monotherapy. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr B03.