|Drug Sub-Category:||Selective oestrogen receptor modulators|
The following information provides a overview of the Tamoxifen and the evidence supporting the categorisation of whether there is a test recommended by our clinical team or not.
|General Comments:||Tamoxifen is given to patients for the treatment of different types of breast cancer, e.g., to prevent the recurrence of oestrogen receptor positive breast cancer, for secondary breast cancers, for ductal carcinoma in situ and in some circumstances to prevent the occurrence of breast cancer.
It is a potent anti oestrogen and acts by competing for the oestrogen receptors in the breast tissue. Consequently it inhibits the effect of oestrogen on tumour growth.
Tamoxifen is processed to several metabolites including endoxifen that is 30-100 times more potent than tamoxifen in its anti-oestrogen effect. It is processed by the enzymes CYP2D6, CYP2C9, CYP2C19, CYP3A4 and CYP2B6.
Several studies have shown that variations in CYP2D6 that cause reduced function were associated with lower endoxifen concentrations. Lower endoxifen concentration has also been associated with a reduced ability to prevent secondary cancer. In addition it was recently shown that breast cancer patients on tamoxifen treatment have a higher chance of disease relapse if they carry one or more non-functioning CYP2D6 genes.
In October 18, 2006 an FDA advisory committee recommended that the FDA includes a warning label that there may be an increased risk of breast cancer recurrence for women with altered CYP2D6 metabolism. Although changes to the labelling has not yet occured, GenesFX Health recommends CYP2D6 testing for breast cancer patients taking tamoxifen.
It is also recommended that co-medication treatment with another drug that is a strong CYP2D6 inhibitor should be avoided. For example Taking drugs that inhibit CYP2D6 (e.g., SSRI antidepressants) has also been associated with lower endoxifen concentrations.
|Apo-Tamox (Canada)||Gen-Tamoxifen (Canada)||Genox (Australia)|
|GenRx TamoxifenTamoxifen-Sandoz (Australia)||ICI-4674 (Alternative Generic Name)||Nolvadex (Australia)|
|Nolvadex-D (Australia)||Nolvadex-D (Canada)||Novadex (Canada)|
|Novadex (United States)||Novo-Tamoxifen (Canada)||NSC 180973 (Alternative Generic Name)|
|Soltamox (United States)||Soltamox (United Kingdom)||TAM (Alternative Generic Name)|
|Tamofen (Canada)||Tamosin (Australia)||Tamoxen (Australia)|
|Tamoxifen (Australia)||Tamoxifen Citrate (Alternative Generic Name)|
|Schroth W, Goetz MP, Hamann U, et al. (2009)||Schroth W, Goetz MP, Hamann U, et al. Association between CYP2D6 polymorphisms and outcomes among women with early stage breast cancer treated with tamoxifen. JAMA. 2009 Oct 7;302(13):1429-36.|