The sustained activation and phosporylation of c-Jun N-terminal kinase (JNK) by reactive oxygen species (ROS) is recognised as one of the crucial mechanisms in the effects of Aplidin on breast cancer cells (Garcia-Fernandez et al, 2002; Cuadrado et al, 2004; Gonzalez-Santiago et al, 2006; Suarez et al, 2006). Here, MAPK8 is linked to breast cancer.