see also:

• breast cancer
• oestrogens
• antioestrogens

• Tamoxifen is the oldest and most-prescribed selective estrogen receptor modulator (SERM) used to treat breast cancer since its approval by US FDA in 1998.
• Tamoxifen won't work on hormone-receptor-negative breast cancer

• cerebral metastases from breast cancer
• tamoxifen related headaches:
  • stroke (CVA)
  • cerebral dural venous sinus thrombosis (CVST) - most at risk in 1st 2 yrs of Rx but rare and usually in those with existing thrombophilia in which case anastrozole should be considered instead of tamoxifen ¹⁾
  • migraine exacerbation at early phase of Rx when peri-menopausal symptoms occur

• increased tumour or bone pain
• menopausal symptoms
• selective oestrogen activation effects
  • stroke (CVA)
  • uterine cancer
    • it appears that tamoxifen activates a cell growth signaling pathway in cells in the uterus
      • in a 2025 study, only 14% of post-tamoxifen uterine cancers harbored cancer-related PIK3CA mutations, compared to 48% of uterine cancers diagnosed in women who hadn’t taken tamoxifen
      • instead, it appears that tamoxifen increases the activity in the P13K-AKT pathway, which regulates uterine cell growth, in part through insulin-like growth factor 1 (IGF1), and that alpelisib, a drug that blocks the P13K pathway and is also used in the treatment of breast cancer appears to reduce this effect and may reduce tamoxifen-induced uterine cancers²⁾
  • rarely:
    • possible precipitation of DVT, pulmonary embolism (PE) or cerebral dural venous sinus thrombosis (CVST) in those with a pre-existing thrombophilia