Tamoxifen and anastrozole are both used in the management of hormone receptor-positive breast cancer, but they have different mechanisms of action:
Tamoxifen:
- Class: Selective estrogen receptor modulator (SERM)
- Mechanism of Action: Tamoxifen either blocks or stimulates oestrogen receptors (ER), depending on the site of action. It blocks oestrogen receptors in breast tissue, and stimulates oestrogen receptors in the uterus and bones. This means it inhibits the stimulatory effect of estrogen on breast cancer cell growth, helps prevent osteoporosis, but it does increase the risk of endometrial cancer.
- Use: It can be used for both premenopausal and postmenopausal women, but it’s especially important for premenopausal women with hormone receptor-positive breast cancer. It is used as adjuvant therapy (treatment after primary therapy) to reduce the risk of breast cancer recurrence. It can also be used for breast cancer prevention in high-risk individuals.
- Duration: Typically prescribed for 5 to 10 years, depending on individual patient factors and the specific clinical scenario.
Anastrozole:
- Class: Aromatase inhibitor
- Mechanism of Action: Aromatase is an enzyme in fat tissue that converts androgens (like testosterone) into estrogens. Anastrozole works by inhibiting the aromatase enzyme, thereby reducing the production of estrogen in postmenopausal women. Since the ovaries in premenopausal women produce a significant amount of estrogen, aromatase inhibitors are generally ineffective in this group.
- Use: It’s primarily used for postmenopausal women with hormone receptor-positive breast cancer, either as initial adjuvant therapy or after 2-3 years of tamoxifen. It’s also used in metastatic breast cancer.
- Duration: Typically prescribed for 5 to 10 years, depending on individual patient factors and the specific clinical scenario.
Both drugs have side effects. For instance, tamoxifen can increase the risk of endometrial cancer and blood clots, while anastrozole can lead to joint pain and an increased risk of osteoporosis.
Tamoxifen or an aromatase inhibitor (Anastrazole, Letrazole) are given for 5 – 10 years to women with oestrogen-receptor positive breast cancer.