MAPK3 and breast cancer: Important in this respect is also that in basal-like breast cancers, the PI3K-AKT and Ras-Raf-MEK-ERK1/2 pathways are often activated, whereas luminal A breast cancers do not show activation of the ERK1/2 pathway, but often contain loss-of-function mutations in the JNK pathway [42,43,44,45].