SCD and breast cancer: In addition, the transcript level of stearoyl COA desaturase (SCD), which catalyzes the rate limiting step in the synthesis of unsaturated fatty acids, and more generally lipid synthesis22, was significantly lower in the sensitive (SKBR3 and MDA-MB-231) BC cells compared to the insensitive (MCF7 and BT474) cells (Fig. 3C).