In renal cell carcinoma, MAPK activation correlated with MAPK kinase activation and Raf-1 activation (Oka et al, 1995), while for hepatocarcinomas a relationship was reported between ERK1/2 activation and expression of the transcription factor c-Fos and cyclin D1 (Ito et al, 1998). Here, FOS is linked to renal cell carcinoma.