Selective oEstrogen Receptor Modulators (SERM)

Tamoxifen is a SERM which acts as an oestrogen receptor antagonist and partial agonist. It is used in the management of oestrogen receptor-positive breast cancer.

Adverse effects

• menstrual disturbance: vaginal bleeding, amenorrhoea
• hot flushes - 3% of patients stop taking tamoxifen due to climacteric side-effects
• venous thromboembolism
• endometrial cancer

Aromatase inhibitors

Anastrozole and letrozole are aromatase inhibitors that reduces peripheral oestrogen synthesis. This is important as aromatisation accounts for the majority of oestrogen production in postmenopausal women and therefore anastrozole is used for ER +ve breast cancer in this group.

Adverse effects

• osteoporosis
  • NICE recommends a DEXA scan when initiating a patient on aromatase inhibitors for breast cancer
• hot flushes
• arthralgia, myalgia
• insomnia