LRPAP1 and breast cancer: ARHI encodes a small GTP-binding protein belonging to the Ras/Rap superfamily, which has the characteristics of a tumor suppressor gene in ovarian and breast cancers, despite sharing 54–59% homology with Ras proto-oncogenes [77], ARHI is expressed in normal breast epithelial cells, but in more than 70% of breast cancers, it is dramatically downregulated.