In human breast cancer MCF7 cells, loss of FADS2 function blocks normal polyunsaturated fatty acid biosynthesis resulting in the FADS1 generation of polyunsaturated fatty acids which lack the 8–9 double bond of eicosanoid signaling precursors (i.e., arachidonic acid and eicosapentaenoic acid) [88]. The gene discussed is FADS2; the disease is breast cancer.