PLXNB1 and basal cell carcinoma: Interestingly, in these cells, Plexin-B2 protein expression was almost lost and Plexin-B1 protein expression was markedly lower than in benign human primary keratinocytes (Fig. 7a), supporting the concept that loss of Plexin-B1/Plexin-B2 could provide a mechanistic basis for basal cell carcinoma progression also in humans.