ESR1 and neoplasm: But, based on our previous work that the general phosphodiesterase inhibitor, dipyridamole inhibits EDI3 activity, viability and tumor growth of ER-HER2+ cells in vitro and in vivo [6], in addition to identifying a specific small molecule inhibitor, we will also investigate existing drugs, for example other phosphodiesterase inhibitors to determine if already available, pharmacologically tested compounds can be repurposed to inhibit EDI3 and tumor growth and metastasis in vivo.