Immunostaining of CD31 (red) in non-small cell lung cancer xenografts. Blue fluorescence indicates DAPI (nuclear) staining. (A) The F0 (control) group exhibited high vessel density. (B) F1, (C) F2 and (D) F3 groups exhibited lower expression of CD31 compared with that in the F0 group. (E) The F4 group demonstrated similar vessel density to that in F0, and higher expression of CD31 compared with that in F1, F2 and F3. CD31, cluster of differentiation 31; F0, mice injected with A549 cells only; F1, mice injected with A549 cells and treated with B20 twice weekly; F2, mice transplanted with F1 tumor explant and treated with B20 twice weekly; F3, mice transplanted with F2 tumor explant and treated with B20 twice weekly; F4, mice transplanted with F3 tumor explant with no treatment.