PDGFRB and neoplasm: These results are consistent with the notion that induction of Arf expression is, for the most part, limited to response to oncogenic signals [4]; however, this analysis did not rule out the possibility of transient induction of Arf expression in the stromal cell types analyzed, nor expression in other classes of tumor infiltrating cells [e.g. Pdgfrβ-negative pericytes [28]].