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Tamoxifen Therapy and Uterine Cancer Risk: The Data and Clinical Implications

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Learning Objectives and CME/Disclosure Information

SUMMARY:

Tamoxifen, a well known SERM, is used to treat breast cancer (hormone receptor positive) because of well-documented benefits including improved disease-free survival (5-year was 38% higher than placebo) and overall survival, regardless of menopausal status. It also is used as a chemoprophylactic agent for women at high risk for breast cancer. ACOG reaffirmed their guidance on tamoxifen monitoring (2019), which includes a statement that tamoxifen use may be extended to 10 years.

Tamoxifen for Breast Cancer Treatment

Uterine Cancer Risk (NSABBP)

  • Within first 5 years of follow up
    • Average annual hazard rate of endometrial cancer: 1.2/1000 patient-years
    • Cumulative hazard rate: 6.3/1000
  • Endometrial cancers following tamoxifen therapy are not of a different type, nor do they carry worse prognosis
  • Authors conclude “net benefit greatly outweighs risk”

Tamoxifen for Breast Cancer Risk Reduction

Uterine Cancer Risk (IBIS-I trial) – 96 month follow-up

  • Endometrial cancer incidence rate
    • Tamoxifen group: 0.59/1000 woman-years
    • Placebo group: 0.38/1000 woman-years
  • Majority FIGO state 1, diagnosed in women >50 years

KEY POINTS:

  • Screening with Transvaginal (TV) Ultrasound
    • Tamoxifen results in subepithelial stromal hypertrophy and therefore makes TV ultrasound screening more difficult and less reliable
    • Routine TV ultrasound and endometrial biopsy for surveillance have “not shown to be effective”
      • May lead to additional unnecessary procedures and is not recommended
    • However, these modalities, including sonohysterography, can be used for follow-up depending on the clinical scenario, especially bleeding
    • Counsel and encourage patients to report any bleeding, spotting, leukorrhea or unusual vaginal discharge
  • Work-up prior to beginning tamoxifen
    • Due to increased risk for polyps, screening and managing uterine polyps prior to tamoxifen initiation can reduce the incidence of atypical hyperplasia
    • The use of progestins to reduce risk for endometrial hyperplasia is not recommended
    • ACOG states that prior to beginning tamoxifen

…there may be a role for pretreatment screening of postmenopausal women with transvaginal ultrasonography, and sonohysterography when needed, or office hysteroscopy

  • Monitoring
    • Postmenopausal
      • Monitor closely “for symptoms of endometrial hyperplasia or cancer”
    • Premenopausal
      • Data does not demonstrate increased risk
      • Routine gyn care
  • If atypical hyperplasia is identified prior to beginning tamoxifen, the patient should be counseled and hysterectomy “should be considered”
    • If endometrial carcinoma occurs and is subsequently managed with hysterectomy, “tamoxifen use may be reinstituted” following consultation with the patient’s breast cancer oncology team

Learn More – Primary Sources:

ACOG Committee Opinion 601: Tamoxifen and Uterine Cancer

Endometrial cancer in tamoxifen-treated breast cancer patients: findings from the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-14

Long-Term Results of Tamoxifen Prophylaxis for Breast Cancer—96-Month Follow-up of the Randomized IBIS-I Trial

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Related ObG Topics:

Endometrial Polyps
Breast Cancer Recurrence Risks Following Endocrine Therapy – 20 Years Out
USPSTF Guidance: When to Use Medication to Reduce Breast Cancer Risk
Endometrial Cancer: The Basics
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