Toremifene

How it works

It competitively binds oestrogen receptors, exerting anti-oestrogenic effects on breast tissue and thereby inhibiting growth of hormone-dependent tumours.

Prescribing in practice

• It prolongs the QT interval in a dose-related manner, so it should be avoided in those with significant QT prolongation, electrolyte disturbance or concurrent QT-prolonging drugs.
• It increases the risk of venous thromboembolism and, like other oestrogen modulators, of endometrial changes, so abnormal vaginal bleeding should be investigated.
• It is metabolised via CYP3A4, so interacting drugs and uncorrected hypokalaemia or hypomagnesaemia should be addressed before and during treatment.

Monitoring

Monitor for cardiac and thromboembolic symptoms, correct electrolyte disturbances, and consider ECG where QT risk factors exist.

Counselling the patient

• Report palpitations, fainting, leg swelling or breathlessness without delay.
• Tell your doctor about any unusual vaginal bleeding.
• Mention all other medicines, as some can affect your heart rhythm when combined with this drug.

Evidence & guidelines

Use is guided by the manufacturer's SPC, with trials showing efficacy comparable to tamoxifen in hormone receptor-positive advanced breast cancer.