Hormonal Therapy

Drug(s) Mechanism of Action
Letrozole, Anastrozole Inhibits cell proliferation and survival by blocking production of estrogen
Tamoxifen, Fulvestrant Inhibits cell proliferation and survival by interfering with estrogen action
Medroxyprogesterone acetate (MPA) Inhibits cell proliferation by inducing apoptosis and growth inhibition
1 2 3 4
  1. Estrogen levels are increased by the conversion of circulating androgen (testosterone) to 17b-estradiol by aromatase produced by the tumor, surrounding stromal tissue, or by other tissues (e.g., adipose).
  2. Estrogen binding to its receptor, ER (estrogen receptor), induces the ER transcriptional activity leading to increased expression of genes involved in cell growth and DNA synthesis.
  3. One of the genes induced by the estrogen-bound ER is the progesterone receptor (PR). Expression of this protein is an indicator of the activity of the ER in the tumor cell.
  4. Anti-estrogens compete with estrogen for binding to the ER and block its full activation, thereby reducing the transcriptional effects of estrogen.

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Green squares, sensitivity markers. Red squares, resistance markers