Tamoxifen-associated endometrial changes

Tamoxifen has pro-oestrogenic effects on the endometrium and thus is associated with an increased prevalence of:

• endometrial polyps: occurs in ~8-36% of women in treated ⁸
• endometrial hyperplasia: occurs in ~1-20% of women treated ^ref
• cystic endometrial atrophy
• endometrial carcinoma

Epidemiology

Up to one-half of breast cancer patients who are treated with tamoxifen may develop an endometrial lesion within 6-36 months. Therefore, any patient who develops bleeding while taking tamoxifen requires evaluation. 

Pathology

Tamoxifen is a non-steroidal "anti-oestrogen" that binds to the oestrogen receptor and is used primarily for adjuvant therapy in breast cancer. However, it can also act as a pro-oestrogen agonist in a low oestradiol environment. The agonist properties can affect the endometrium, and does, in a high percentage of patients (50%).

Radiographic features 

Ultrasound

Tamoxifen may cause the endometrium to appear thickened, irregular, and cystic.  Most patients tend to have a multiplicity of findings. 

• normal endometrial thickness despite tamoxifen use, i.e. <5 mm (although ~50% of those receiving tamoxifen have been reported to have a thickness of >8 mm ²
  • it has also been reported that the degree of endometrial thickening corresponds to the duration of tamoxifen therapy
• subendometrial cysts
• endometrial polyps
  • usually larger than in untreated women 
  • sonohysterography may be useful for their identification

Treatment and prognosis

Ultrasound screening of asymptomatic patients taking tamoxifen has been shown to be problematic due to a high number of false positives. It is thusnot recommended routine ultrasound is performed for screening if a lady on tamoxifen is not experiencing bleeding.

It has been proposed that patients taking tamoxifen who present with vaginal bleeding should go directly to hysteroscopy and endometrial biopsy ⁷.