MAPK3 and breast cancer: Elevated ERK1/2 activity has been noted in a proportion of clinical breast cancers vs benign disease or cancer-associated normal epithelium (Sivaraman et al, 1997; Santen et al, 2002), and a relationship between elevated MAPK activity and shorter disease-free survival in primary breast cancer has been reported (Mueller et al, 2000; Gee et al, 2001; Adeyinka et al, 2002).