Tumor perivascular PDGFBR as an independent prognostic factor in metastatic colorectal cancer.

Abstract

3571 Background: New vessel formation is an essential factor for tumor growth and metastasis. Tumor vessels show reduced and variable pericyte coverage. Several pericyte markers have been identified, including platelet-derived growth factor receptor beta (PDGFbR), smooth muscle α-actin (ASMA) and desmin. Variability in pericyte status and its prognostic significance remains largely uncharacterized in colorectal cancer (CRC). The aim of the present study was to perform a preliminary analysis of the variability in expression of the three pericyte markers and to investigate the potential prognostic significance of perivascular PDGFbR (PV-PDGFbR). Methods: A population-based cohort was used for double-staining, performed on 100 tumors with CD34 and above-named pericyte markers. For the rest of the study a metastatic CRC (mCRC) collection from the phase III NORDIC-VII study was used. Analyses were performed on a tissue microarray with tumor material from 328 out of the 566 patients in the intention to treat population. All tumors and corresponding normal tissue were scored by immunohistochemistry (IHC) with regard to PV-PDGFbR. 255 and 97 cases were analyzed by IHC with regard to perivascular ASMA and microvessel density (MVD), respectively. Results: Analyses of the double-staining revealed independent and variable expressions of all three pericyte markers. Analyses of the NORDIC-VII cohort revealed two prognostic groups with low and high PV-PDGFbR expression. Median OS was 14.3 mo for PV-PDGFbR-low tumors (N=22) vs. 22.9 mo for PV-PDGFbR-high (N=306) tumors (HR=1.95; 95% CI 1.20-3.16; log-rank p=0.007). Multivariate analysis, including WHO performance status, alkaline phosphatase level and BRAF mutation status confirmed PV-PDGFbR as an independent prognostic factor of OS (HR=1.75; 95% CI 1.07-2.84; p=0.025). PV-PDGFbR was not significantly linked to perivascular ASMA or MVD. PV-PDGFbR in normal tissue was not associated with survival. Conclusions: CRC display a previously un-recognized variability in pericyte characteristics. Low tumor PV-PDGFbR level is associated with worse prognosis in patients with mCRC, in a manner independent of performance status, alkaline phosphatase levels and BRAF status.