Thus, we tested sensitivity to SFN of four established breast cancer cell lines which have distinct characteristics regarding the status of the pathway elements: MDA MB 231 is estrogen-independent cell line with low level of ErbB2 and EGFR1 receptors, MCF-7 is estrogen receptor (ER) positive cell line with low level of ErbB2 and EGFR1 receptors, MDA MB 468 cells are devoid of PTEN repressor (negative regulator of the PI3K-Akt-mTOR signaling) and possess high EGFR1 level and SKBR-3 cells overproduce receptor kinase ErbB2 [23–25] (Table 1). The gene discussed is ESR1; the disease is breast carcinoma.