While the prototype oestrogen receptor blocker that increased survival in breast cancer, by reducing the risk of developing invasive estrogen receptor-positive breast cancer by 49% it is increasingly being replaced by aromatase inhibitors due to better overall effectiveness. This is partially due to their better side effect profile and the several potential metabolic interactions that on theoretical grounds might be expected to reduce tamoxifen's effectiveness with commonly co-administered drugs, but have been difficult to demonstrate.
- Oestrogen-receptor positive breast cancer
- Adjuvant treatment early breast cancer 20mg od
- In locally advanced or metastatic breast cancer up to 40mg a day.
- Will be protective against osteoporotic fractures. The epidemiological and trial evidence overwhelming favours its place in long term therapy in estrogen receptor-positive breast cancer despite its side effect profile.
Cautions and Interactions
- Monitor for endometrial pathology
- Baseline opthalmological assessment and reconsider therapy if cataracts and retinopathy develop
- Interaction via it is believed CYP3A4 and CYP2D6 with now both interactions having evidence of clinical significance:
- VTE risk increased by at least twice (even more if given at same time as systemic chemotherapy)
- Anaemia, neutropenia and thrombocytopenia
- Hot flushes
- Fluid retention
- Vaginal discharge
- Nausea and vomiting
Competes for the binding sites with estradiol. Reduces total cholesterol and low density lipoproteins. Increases steroid- and thyroxine-binding proteins. Reduces antithrombin III. N-desmethyltamoxifen is the principal metabolite.
- ↑ Waters EA, Cronin KA, Graubard BI, Han PK, Freedman AN. Prevalence of tamoxifen use for breast cancer chemoprevention among u.s. Women. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology. 2010 Feb; 19(2):443-6.(Link to article – subscription may be required.)
- ↑ Brewster AM, Christo DK, Lai H, Helzlsouer K. Breast carcinoma chemoprevention in the community setting. Estimating risks and benefits. Cancer. 2005 Mar 15; 103(6):1147-53.(Link to article – subscription may be required.)
- ↑ Kelly CM, Juurlink DN, Gomes T, Duong-Hua M, Pritchard KI, Austin PC, Paszat LF. Selective serotonin reuptake inhibitors and breast cancer mortality in women receiving tamoxifen: a population based cohort study. BMJ (Clinical research ed.). 2010; 340:c693.(Epub)