Moreover, it has recently been shown that AR-null prostate cancers that do not undergo neuroendocrine differentiation, or ‘double negative’ metastatic prostate cancers have sustained FGF-MAPK signaling and that these cancers are sensitive to MEK and ERK1/2 inhibition in vitro and in vivo [58]. Here, MAPK3 is linked to metastatic prostate carcinoma.