Although the data presented here strongly suggest a role for FKBPL as a potent antiangiogenic mediator, our previous data also supports a role for FKBPL as an intracellular regulator of estrogen receptor signaling through its association with Hsp90.13 Therefore, the FKBPL-mediated effects on the embryonic lethality, the differences in our mouse and zebrafish data and perhaps why tumor growth rates in our FKBPL-deficient mice are higher, might also suggest a role for FKBPL-mediated regulation of estrogen receptor signaling. This evidence concerns the gene FKBPL and neoplasm.