To highlight the validity of this effect in vivo, we performed CD31 staining on sections of treated tumors, and found that palbociclib treatment caused a notable decrease in angiogenesis by CD31 when compared to vehicle control, implicating the microenvironment of the tumor as having a role in the efficacy of palbociclib (Supplemental Fig. 4A, B). The gene discussed is PECAM1; the disease is neoplasm.