Notably, genes specifically upregulated by SUMO-deficient PR (that is, phospho-PR driven) are significantly associated with genes that are highly expressed in ERBB2-positive human breast tumors and cell lines; our studies support a mechanistic link between phosphorylated (deSUMOylated) PR-B-specific transcriptional action and expression of a subset of ERBB2-associated genes (Figure 5). This evidence concerns the gene RB1 and breast neoplasm.