Tamoxifen: Targeted Estrogen Receptor Modulation for Breast Cancer
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Synonyms
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Tamoxifen is a selective estrogen receptor modulator (SERM) widely utilized in the management of hormone receptor-positive breast cancer. It functions by competitively inhibiting estrogen binding at receptor sites, thereby impeding the proliferative signals that fuel certain breast cancer cells. This agent is indicated for both early and advanced stages of breast carcinoma in pre- and postmenopausal women, as well as for risk reduction in high-risk individuals. Its well-established efficacy and manageable safety profile have made it a cornerstone of endocrine therapy for decades.
Features
- Active ingredient: Tamoxifen citrate
- Drug class: Selective estrogen receptor modulator (SERM)
- Available forms: Oral tablets (10 mg and 20 mg)
- Prescription status: Requires medical prescription
- Mechanism: Antagonizes estrogen receptors in breast tissue
Benefits
- Significantly reduces the risk of recurrence in early-stage, hormone receptor-positive breast cancer
- Lowers the incidence of contralateral breast cancer
- Provides an effective endocrine treatment option for premenopausal women
- Can be used as a chemopreventive agent in high-risk patients
- Offers oral administration convenience for long-term therapy
- Demonstrates a generally favorable tolerability profile with long-term use
Common use
Tamoxifen is primarily indicated for the treatment of hormone receptor-positive breast cancer in both early and advanced disease settings. It is used as adjuvant therapy following primary treatment (surgery, radiation, or chemotherapy) to reduce the risk of cancer recurrence. Additionally, it is employed for metastatic breast cancer management and for risk reduction in women with a high risk of developing breast cancer. Off-label uses include treatment of gynecomastia and other estrogen-related conditions under specialist supervision.
Dosage and direction
The standard dosage for breast cancer treatment is 20 mg orally once daily, though doses may range from 20-40 mg daily based on individual patient factors and clinical context. For breast cancer risk reduction, the typical dose is 20 mg daily for five years. Administration should occur at approximately the same time each day, with or without food. Tablets should be swallowed whole with water. Treatment duration is typically 5-10 years as determined by the treating oncologist based on individual risk assessment and response.
Precautions
Patients should undergo regular gynecological examinations due to increased risk of endometrial changes. Regular monitoring of liver function is recommended. Caution is advised in patients with history of thromboembolic events. Women of childbearing potential should use non-hormonal contraception during treatment. Regular ophthalmologic examinations are recommended for patients on long-term therapy. Patients should be monitored for symptoms of depression or mood changes.
Contraindications
Hypersensitivity to tamoxifen or any component of the formulation. Concomitant warfarin therapy in patients with history of deep vein thrombosis or pulmonary embolism. Pregnancy and breastfeeding. Use in patients with history of endometrial cancer. Concurrent aromatase inhibitor therapy. Patients with active hepatic disease or significant hepatic impairment.
Possible side effect
Common side effects include hot flashes (≥10%), vaginal discharge or dryness (5-10%), and nausea (5-10%). Less frequently reported effects include menstrual irregularities, fatigue, and mood swings. Serious but rare adverse reactions include endometrial cancer (<1%), thromboembolic events (1-2%), and ocular changes including cataracts (1-3%). Most side effects are dose-dependent and often diminish with continued therapy.
Drug interaction
Strong CYP2D6 inhibitors (e.g., paroxetine, fluoxetine) may reduce tamoxifen efficacy. Warfarin coadministration increases anticoagulant effect requiring close INR monitoring. Aromatase inhibitors may antagonize tamoxifen’s effects. CYP3A4 inducers (e.g., rifampin) may decrease tamoxifen concentrations. Tamoxifen may enhance the thrombogenic potential of estrogen-containing therapies.
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next scheduled dose. In that case, skip the missed dose and resume the regular dosing schedule. Do not double the dose to make up for a missed dose. Maintain consistent daily timing for optimal therapeutic effect.
Overdose
Acute overdose may manifest as tremor, hyperreflexia, unsteady gait, dizziness, or nausea. There is no specific antidote for tamoxifen overdose. Treatment should be symptomatic and supportive. Gastric lavage may be considered if presented early after ingestion. Monitor for QT prolongation and provide cardiac monitoring if large overdose is suspected.
Storage
Store at controlled room temperature (20-25°C or 68-77°F). Protect from light and moisture. Keep in original container with lid tightly closed. Keep out of reach of children and pets. Do not use after expiration date printed on packaging.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Treatment decisions should be made in consultation with a qualified healthcare professional. Individual response to therapy may vary. Always follow the prescribed dosage and instructions provided by your treating physician.
Reviews
Clinical studies demonstrate tamoxifen reduces breast cancer recurrence by 40-50% in hormone receptor-positive disease. Long-term follow-up data from major trials (NSABP B-14, IBIS-I) show sustained benefit with 5 years of therapy. Patient-reported outcomes indicate generally good quality of life during treatment, though vasomotor symptoms remain a common challenge. Ongoing research continues to refine patient selection and duration recommendations.