PDGFD and essential thrombocythemia: In the ET group, high malignancy grade (P < 0.001), the presence of vascular invasion (P = 0.011), non-wide resection margins (P = 0.039) and high expression of PDGF-D (HR = 1.863, 95% CI = 1.057-3.283, P = 0.031) were significant independent prognostic indicators of DSS.