Abstract
A robust immunohistochemical (IHC) assay for VEGFR2 was developed to investigate its utility for patient tailoring in clinical trials. The sensitivity, specificity, and selectivity of the IHC assay were established by siRNA knockdown, immunoblotting, mass spectrometry, and pre-absorption experiments. Characterization of the assay included screening a panel of multiple human cancer tissues and an independent cohort of non-small cell lung carcinoma (NSCLC, n = 118) characterized by TTF-1, p63, CK5/6, and CK7 IHC. VEGFR2 immunoreactivity was interpreted qualitatively (VEGFR2 positive/negative) in blood vessels and by semi-quantitative evaluation using H-scores in tumor cells (0–300). Associations were determined among combinations of VEGFR2 expression in blood vessels and tumor cells, and clinico-pathologic characteristics (age, sex, race, histologic subtype, disease stage) and overall survival using Kaplan-Meier analyses and appropriate statistical models. VEGFR2 expression both in blood vessels and in tumor cells in carcinomas of the lung, cervix, larynx, breast, and others was demonstrated. In the validation cohort, 99/118 (83.9%) NSCLC tissues expressed VEGFR2 in the blood vessels and 46/118 (39.0%) showed high tumor cell positivity (H-score ≥10). Vascular and tumor cell expression were inversely correlated (p = 0.0175). High tumor cell expression of VEGFR2 was associated with a 3.7-fold reduction in median overall survival in lung squamous-cell carcinoma (SCC, n = 25, p = 0.0134). The inverse correlation between vascular and tumor cell expression of VEGFR2 and the adverse prognosis associated with high VEGFR2 expression in immunohistochemically characterized pulmonary SCC are new findings with potential therapeutic implications. The robustness of this novel IHC assay will support further evaluation of its utility for patient tailoring in clinical trials of antiangiogenic agents.
Highlights
Vascular endothelial cell growth factor (VEGF) is a potent mitogen and specific mediator of angiogenesis
We have developed an analytically robust IHC assay for determination of VEGFR2 expression on archival human tumor tissues using a technically sound assay development and optimization approach that included high quality human tissues, confirmation of assay specificity and selectivity, stringent quality control, and analytical validation
Immunoreactivity for VEGFR2 was localized to the cytoplasm of the endothelial cells but was present in tumor cells from several histologic subtypes of human malignancies
Summary
Vascular endothelial cell growth factor (VEGF) is a potent mitogen and specific mediator of angiogenesis. VEGF/VEGFR2 expression and microvessel density are correlated in several tumor types. This increased microvessel density is associated with poor prognosis in patients with a variety of carcinomas including non-small cell lung cancer (NSCLC) [5]. In early phase clinical studies, a recombinant human monoclonal antibody (IgG1) that binds to the extracellular domain of human VEGFR2, ramucirumab (IMC-1121B [LY3009806]), has demonstrated preliminary evidence of efficacy in a variety of human tumors including NSCLC, renal carcinoma, hepatocellular carcinoma, melanoma, ovarian cancer, and colorectal cancer [8,9,10,11,12,13]
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