Even though studies have reported that stripping fetal bovine serum removed important factors like thyroid hormones and vitamins which may affect the growing conditions of breast cancer cells [21], our studies demonstrate that addition of T4 (L-thyroxine) with concentrations of 0.001 to 1 μM after stripping did not significantly alter the levels of ERα or p53. The gene discussed is TP53; the disease is breast cancer.