For instance, Mandal et al. capped the phosphate oxygen atoms of a high-affinity STAT3 binding phosphopeptide with an enzyme-cleavable group—pivaloyloxymethyl (POM)—and replaced the phosphate with a phosphonodifluoromethyl moiety to create phosphatase-stable, cell-permeable peptidomimetic prodrugs that inhibited the phosphorylation of STAT3 in breast cancer cell lines [63]. This evidence concerns the gene STAT3 and breast cancer.