Boswellia sacra essential oil-regulated signaling molecules activation and cell cycle-related proteins expression in human breast cancer cells. Breast cancer cells were seeded at the concentration of 5 × 105 cells/60 mm tissue culture plate. After adherence, cells were treated with either 1:800 dilution of 78 oC or 1:1,200 dilution of 100 oC essential oil. Total cellular proteins were isolated between 0 (untreated control) and 4 hours following essential oils treatment. Western blot analysis was performed to determine levels of Akt and ERK1/2 phosphorylation as well as cyclin D1 and cdk4 proteins expression. Expression of β-actin was also determined in parallel and used as a protein loading control. Experiments were repeated at least twice for each cell line and representative results are presented.