We found that, with or without insulin or estradiol stimulation, DHA had no effect on the pERK1/2/ERK1/2 ratio, but reduced the pAkt/Akt and pS6/S6 ratios and p-SREBP-1, m-SREBP-1, and FASN expression in, and proliferation of, MCF-7 human breast cancer cells. This evidence concerns the gene MAPK3 and breast cancer.