Tamoxifen

Tamoxifen is used to treat breast cancer that has spread to other parts of the body (metastatic breast cancer), to treat breast cancer in certain patients after surgery and radiation therapy, and to reduce the chances of breast cancer in high-risk patients.

Tamoxifen can block the growth of breast cancer. It works by interfering with the effects of estrogen in the breast tissue.

Tamoxifen is available under the following different brand names: Soltamox.

Dosage Forms and Strengths

Tablet (generic)

• 10 mg
• 20 mg

Oral solution

• 10mg/5mL (Soltamox)

Dosage Considerations – Should be Given as Follows:

Breast Cancer Treatment

• 20-40 mg/day orally; doses greater than 20mg/day should be divided twice daily (i.e., morning and evening)
• Although the FDA has approved a dosage range of 20-40 mg/day, clinical benefit for doses greater than 20 mg/day has not been demonstrated
• Continue with adjuvant therapy for at least 5 years
• For women with ER-positive disease, continuing tamoxifen to 10 years rather than stopping at 5 years produces a further reduction in recurrence and mortality, particularly after year 10 (ATLAS trial, Lancet 2013;381:805-816; aTTom trial; ASCO Annual Meeting 2013;31:5)
• Treatment indications:
  • Treatment of metastatic breast cancer in women and men; in premenopausal women, alternative to oophorectomy or ovarian irradiation; estrogen receptor positive tumors more likely to benefit
  • Adjuvant treatment of node-positive breast cancer in postmenopausal women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation; most benefit in the subgroup with 4 or more positive axillary nodes
  • Adjuvant treatment of axillary node-negative breast cancer in women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation
  • Reduces occurrence of contralateral breast cancer in patients receiving adjuvant treatment

Breast Cancer Treatment

• 20-40 mg/day orally; doses greater than 20mg/day should be divided twice daily (i.e., morning and evening)
• Although the FDA has approved a dosage range of 20-40 mg/day, clinical benefit for doses greater than 20 mg/day has not been demonstrated
• Continue with adjuvant therapy for at least 5 years
• For women with ER-positive disease, continuing tamoxifen to 10 years rather than stopping at 5 years produces a further reduction in recurrence and mortality, particularly after year 10 (ATLAS trial, Lancet 2013;381:805-816; aTTom trial; ASCO Annual Meeting 2013;31:5)
• Treatment indications:
  • Treatment of metastatic breast cancer in women and men; in premenopausal women, alternative to oophorectomy or ovarian irradiation; estrogen receptor positive tumors more likely to benefit
  • Adjuvant treatment of node-positive breast cancer in postmenopausal women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation; most benefit in the subgroup with 4 or more positive axillary nodes
  • Adjuvant treatment of axillary node-negative breast cancer in women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation
  • Reduces occurrence of contralateral breast cancer in patients receiving adjuvant treatment

Ductal Carcinoma in Situ (DCIS)

• Indicated in women with ductal carcinoma in situ following breast surgery and radiation to reduce the risk of invasive breast cancer
• 20 mg orally once/day for 5 years

Breast Cancer Prevention

• Indicated to reduce the incidence of breast cancer in women at high risk for breast cancer; high risk is defined as women aged 35 years or older with a 5-year predicted risk of breast cancer 1.67% or more (calculated by the Gail Model)
• 20 mg orally once/day for 5 years
• Data are limited for use greater than 5 years in the risk-reduction setting (NCCN guidelines)

Ovulation Induction (Off-label)

• 5-40 mg orally every 12 hours for 4 days

Mastalgia (Off-label)

• 10 mg orally once/day for 4 months

Other Indications and Uses

• Gynecomastia

Common side effects or health problems may include:

• Abdominal cramps
• Absence of menstrual periods
• Bone pain
• Cataracts
• Changes in menstrual periods
• Cough
• Depression
• Difficulty having an orgasm
• Dizziness
• Fatigue
• Fluid retention
• Hair thinning
• Headache
• Hot flashes
• Impotence
• Infrequent or light menstrual periods
• Joint pain
• Leg cramps
• Loss of appetite
• Muscle aches
• Musculoskeletal pain
• Nausea
• Ovarian cyst
• Swelling (edema) in your hands or feet
• Fluid retention
• Tumor pain
• Vaginal discharge
• Vaginal itching or dryness
• Weight loss

Less common side effects of tamoxifen include:

• Skin swelling
• Corneal changes
• Loss of sex drive (libido)/decreased sexual ability
• Endometrial cancer
• Pancreatitis
• Retinal vein thrombosis
• Stroke
• Uterine fibroids

This is not a complete list of side effects and other serious side effects or health problems may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of this medicine or any drug before seeking medical advice from your doctor, healthcare provider or pharmacist first. To do so may result in serious consequences or side effects.

• Severe Interactions of tamoxifen include:
  • none
• Tamoxifen has serious interactions with at least 23 different drugs.
• Tamoxifen has moderate interactions with at least 101 different drugs.
• Mild Interactions of tamoxifen include:
  • aprepitant
  • artemether/lumefantrine
  • black cohosh
  • butalbital
  • divalproex sodium
  • eucalyptus
  • fluconazole
  • lapatinib
  • maitake
  • marijuana
  • mephobarbital
  • nifedipine
  • ruxolitinib
  • sitaxentan
  • taurine
  • troleandomycin
  • wheat germ extract

This document does not contain all possible interactions from the use of this medication. Therefore, before using this drug, tell your doctor or pharmacist of all the drugs you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

Warnings

• For women with ductal carcinoma in situ (DCIS) and women at high risk for breast cancer: Uterine malignancies, stroke, and pulmonary embolism reported with use in risk-reduction setting (women with ductal carcinoma in situ and women at high risk for breast cancer).
• This medication contains tamoxifen. Do not take Soltamox if you are allergic to tamoxifen or any ingredients contained in this drug.
• Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Contraindications

• Hypersensitivity
• Pregnancy (see "Pregnancy and Lactation" section)
• Undiagnosed vaginal bleeding
• History of thromboembolism (prevention, ductal carcinoma in situ [DCIS])
• Coumarin/Coumadin anticoagulation (prevention, ductal carcinoma in situ [DCIS])

Effects of Drug Abuse

• No information provided

Short-Term Effects

• See "What Are Side Effects Associated with Using Tamoxifen?"

Long-Term Effects

• Chronic use for prevention may result in increased risk of stroke, pulmonary embolism, endometrial cancer, uterine sarcoma, and cataracts.
• See "What Are Side Effects Associated with Using Tamoxifen?"

Cautions

• History of thromboembolism (CA treatment); tamoxifen significantly increases risk of venous thromboembolism.
• Coumarin/Coumadin anticoagulation (CA treatment).
• CYP2D6 polymorphism-CYP2D6 converts tamoxifen to active metabolite endoxifen; lowered CYP2D6 activity or concomitant CYP2D6 inhibitors may reduce tamoxifen efficacy.
• Bone metastases.
• Low blood platelet count (thrombocytopenia).
• Cholestasis, fatty liver, hepatic necrosis, and hepatitis reported.
• Low white blood cell count (leukopenia).
• Postmarketing cases of hyperlipidemia reported.
• Decreased visual acuity, corneal changes, retinal vein thrombosis.
• Flushing and increased bone pain and/or tumor pain sometimes associated with good tumor response.
• Chronic use for prevention may result in increased risk of stroke, pulmonary embolism, endometrial cancer, uterine sarcoma, and cataracts.
• Avoid pregnancy. Pregnancy (see "Pregnancy and Lactation" section)

Pregnancy and Lactation

• Use tamoxifen during pregnancy only in LIFE-THREATENING emergencies when no safer drug is available. There is positive evidence of human fetal risk.
• It is not known if tamoxifen is excreted in breast milk. Do not nurse while using tamoxifen.