PECAM1 and neoplasm: An immunofluorescence-based colocalization study showed colocalization of D2R and CD31, indicating that endothelial cells express D2R in both MSK-LX40 and MSK-LX40R tumour tissues, although endothelial D2R expression was lower in vehicle-treated chemotherapy-resistant MSK-LX40R tumour tissues than in vehicle-treated chemotherapy-sensitive MSK-LX40 specimens (see vehicle-treated group in Fig. 7d; Supplementary Fig. 9), similar to our observation in paired chemotherapy-naïve and chemotherapy-resistant specimens from the cohort of SCLC-A patients (Fig. 6).