[¹⁸F]FDG PET/CT Signal Correlates with Neoangiogenesis Markers in Patients with Fibrotic Interstitial Lung Disease Who Underwent Lung Biopsy: Implication for the Use of PET/CT in Diffuse Lung Diseases.

Abstract

The use of [¹⁸F]FDG PET/CT as a biomarker in diffuse lung diseases is increasingly recognized. We investigated the correlation between [¹⁸F]FDG uptake with histologic markers on lung biopsy of patients with fibrotic interstitial lung disease (fILD). <b>Methods:</b> We recruited 18 patients with fILD awaiting lung biopsy for [¹⁸F]FDG PET/CT. We derived a target-to-background ratio (TBR) of maximum pulmonary uptake of [¹⁸F]FDG (SUV_max) divided by the lung background (SUV_min). Consecutive paraffin-embedded lung biopsy sections were immunostained for alveolar and interstitial macrophages (CD68), microvessel density (MVD) (CD31 and CD105/endoglin), and glucose transporter 1. MVD was expressed as vessel area percentage per high-power field (Va%/hpf). Differences in imaging and angiogenesis markers between histologic usual interstitial pneumonia (UIP) and non-UIP were assessed using a nonparametric Mann-Whitney test. Correlation of imaging with angiogenesis markers was assessed using the nonparametric Spearman rank correlation. Univariate Kaplan-Meier survival analysis assessed the difference in the survival curves for each of the angiogenesis markers (separated by their respective optimal cutoff) using the log-rank test. Statistical analysis was performed using SPSS. <b>Results:</b> In total, 18 patients were followed for an average of 41.36 mo (range, 5.69-132.46 mo; median, 30.07 mo). Only CD105 MVD showed a significantly positive correlation with [¹⁸F]FDG TBR (Spearman rank correlation, 0.556; <i>P</i> < 0.05, <i>n</i> = 13). There was no correlation between [¹⁸F]FDG uptake and macrophage expression of glucose transporter 1. CD105 and CD31 were higher for UIP than for non-UIP, with CD105 reaching statistical significance (<i>P</i> = 0.011). In all patients, MVD assessed with either CD105 or CD31 quantification on biopsy predicted overall survival. Patients with CD105 MVD of less than 12 Va%/hpf or CD31 MVD of less than 35 Va%/hpf had a significantly better prognosis (no deaths during follow-up in the case of CD105) than did patients with higher scores of CD105 MVD (median survival, 35 mo; <i>P</i> = 0.041, <i>n</i> = 13) or CD31 MVD (median survival, 28 mo; <i>P</i> = 0.014, <i>n</i> = 13). <b>Conclusion:</b> Previous work has used [¹⁸F]FDG uptake in PET/CT as a biomarker in fILD. Here, we highlight a correlation between angiogenesis and [¹⁸F]FDG TBR. We show that MVD is higher for UIP than for non-UIP and is associated with mortality in patients with fILD. These data set the scene to investigate the potential role of vasculature and angiogenesis in fibrosis.