Endocrine Therapy for Breast Cancer with Tamoxifen

  • Tamoxifen is indicated for:
    • Premenopausal patients with:
      • Node-negative, hormone receptor–positive, HER2-negative breast cancer with low-risk recurrence scores
  • Tamoxifen:
    • Is a selective estrogen receptor modulator (SERM) with antiestrogenic activity in breast tissue:
      • Reducing epithelial cell proliferation
  • Hot flashes are one of the most common and bothersome side effects of tamoxifen:
    • Up to 80% of women prescribed tamoxifen complain of hot flashes:
      • About 30% rate them as severe
    • Premenopausal women have a greater increase in hot flashes after starting tamoxifen compared with perimenopausal or postmenopausal women
    • Hot flashes are believed to be due to:
      • A central nervous system antiestrogenic effect:
        • Causing thermoregulatory dysfunction
    • Additionally, some data suggest that polymorphisms in drug metabolizing enzymes:
      • Cytochrome P450 enzyme, CYP2D6):
        • Decrease the conversion of tamoxifen to its most active metabolite (endoxifen), and they may influence the likelihood of tamoxifen-related hot flashes
    • Coadministration of drugs that inhibit the activity of CYP2D6:
      • Such as the selective serotonin reuptake inhibitors (SSRIs):
        • Can reduce tamoxifen-related hot flashes
      • Among SSRIs, there is a gradient of potency for inhibition of CYP2D6:
        • For example, paroxetine and fluoxetine are strong CYP2D6 inhibitors, while sertraline and duloxetine are moderate inhibitors
        • While the strong CYP2D6 inhibitors have the potential to adversely affect drug efficacy:
          • The data to suggest that this issue decreases tamoxifen effect are very weak
        • Venlafaxine:
          • Is a weak CYP2D6 inhibitor with proven efficacy against hot flashes without risk of significantly interfering with tamoxifen metabolism
  • Black cohosh is a substance with purported efficacy treating menopausal symptoms:
    • It is not FDA regulated with reported rare incidence of hepatotoxicity
    • Its use would be contraindicated in a patient on tamoxifen:
      • As it may interfere with CYP2D6 activity

References

1. Aiello Bowles EJ, Boudreau DM, Chubak J, Yu O, Fujii M, Chestnut J, Buist DS. Patient-reported discontinuation of endocrine therapy and related adverse effects among women with early-stage breast cancer. J Oncol Pract. 2012;8(6):e149-e157.

2. Ramaswami R, Villarreal MD, Pitta DM, Carpenter JS, Stebbing J, Kalesan B. Venlafaxine in management of hot flashes in women with breast cancer: a systematic review and meta-analysis. Breast Cancer Res Treat. 2015;152(2):231-237.

3. Johns C, Seav SM, Dominick SA, Gorman JR, Li H, Natarajan L, Mao JJ, et al. Informing hot flash treatment decisions for breast cancer survivors: a systematic review of randomized trials comparing active interventions. Breast Cancer Res Treat. 2016;156(3):415-426.

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