Exposition of MDA-MB-231 and MCF-7 human breast cancer cell lines to fish oil high in DHA caused upregulation of PTEN tumor suppressor protein and subsequently inhibited the expression of CSF-1 (colony-stimulating factor-1) potent activator of malignancy and metastasis and its secretion from cancer cells through PI 3 kinase/Akt signaling. The gene discussed is CSF1; the disease is breast cancer.