Despite the fact that multiple naturally occurring mutations have been identified in Ras, Raf1 and MEK which largely contribute to the elevated activation of the MAPK pathway in many other types of cancer [13], these oncogenic mutations are infrequent in prostate cancer patients and the molecular mechanisms underlying the hyperactivation of Raf1/MEK/ERK1/2 pathway in prostate cancer remain poorly defined. Here, MAPK3 is linked to Familial prostate cancer.