Tamoxifen
A SERM that blocks estrogen in breast tissue, used to treat and prevent estrogen receptor-positive breast cancer.
Drug card
- Class
- SERM
- How it works
- Binding estrogen receptors to block estrogen in breast but mimic it in bone
- Used for
- Estrogen receptor-positive breast cancer, early or advanced
- Lowering breast cancer risk in high-risk women or after DCIS
- Known for
- Hot flashes
- Endometrial cancer and uterine sarcoma
- Blood clots (deep vein thrombosis, pulmonary embolism)
- Its name
- -ifene, -ifen means an estrogen receptor modulator (tamoxifen type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does tamoxifen work?
Tamoxifen competes with estradiol for the estrogen receptor and blocks estrogen-driven growth of breast cancer cells, while acting like estrogen on the endometrium and bone. CYP2D6 turns it into endoxifen and 4-hydroxytamoxifen, metabolites that bind the receptor about 100 times more tightly than tamoxifen itself.
Uses
What is tamoxifen used for?
- Estrogen receptor-positive breast cancer, early or advanced
- Lowering breast cancer risk in high-risk women or after DCIS
Side effects
Side effects of tamoxifen
- Hot flashesKnown for
- Endometrial cancer and uterine sarcomaKnown forSerious
- Blood clots (deep vein thrombosis, pulmonary embolism)Known forSerious
- StrokeSerious
- Irregular periods, vaginal bleeding or discharge
- Cataracts
- Retinopathy and other eye changes
- Liver damage, and rarely liver cancerSerious
- Fluid retention
- Mood changes and depression
- High calcium early on, with bone metastasesSerious
- Harm to the fetusSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated with warfarin or a past DVT or PE when used for risk reduction; otherwise warfarin's effect rises and needs close INR checks.
- Abnormal vaginal bleeding is investigated promptly because of the endometrial cancer risk.
- Strong CYP2D6 inhibitors such as paroxetine may lower levels of its active metabolites and so its benefit.
- Pregnancy: it can harm the fetus, so effective nonhormonal contraception is needed.
Good to know: Used both before and after menopause, unlike aromatase inhibitors, which work only after menopause or with ovarian suppression.
Remember it
A way to remember it
Breast blocker, bone protector
SERMs block estrogen in breast tissue but act like estrogen in bone, so raloxifene treats osteoporosis; tamoxifen also acts like estrogen on the womb lining, which explains its endometrial cancer risk.
Written for biofideX
Its name
-ifene, -ifen means estrogen receptor modulator (tamoxifen type)
Raloxifene and clomifene end in -ifene; tamoxifen keeps the older -ifen. Tamoxifen and raloxifene block estrogen receptors in some tissues and stimulate them in others.
- Every drug name stem
Its class
Selective estrogen receptor modulators
SERMs bind estrogen receptors and act as estrogen in some tissues but block it in others, depending on whether the bound receptor recruits coactivators or corepressors there. Tamoxifen and raloxifene block estrogen in the breast, which treats or prevents receptor-positive breast cancer, and act like estrogen on bone. Tamoxifen also stimulates the endometrium; raloxifene does not.
Easily mixed up with aromatase inhibitors and estrogens.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Tamoxifen citrate oral solution: label (DailyMed)
- Tamoxifen (NCI Thesaurus)
- Tamoxifen Citrate (NCI)
- Hormone Therapy for Breast Cancer (NCI)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Targeted therapy and the immune system
Tamoxifen is one of 13 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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