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Genotype of metabolic enzymes and the benefit of tamoxifen in postmenopausal breast cancer patients
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Oncology . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Oncology . Linköping University, Faculty of Health Sciences.
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2005 (English)In: Breast Cancer Research, ISSN 1465-5411(print), 1465-542X (online), Vol. 7, no 3, R284-R290 p.Article in journal (Refereed) Published
Abstract [en]


Tamoxifen is widely used as endocrine therapy for oestrogen-receptor-positive breast cancer. However, many of these patients experience recurrence despite tamoxifen therapy by incompletely understood mechanisms. In the present report we propose that tamoxifen resistance may be due to differences in activity of metabolic enzymes as a result of genetic polymorphism. Cytochrome P450 2D6 (CYP2D6) and sulfotransferase 1A1 (SULT1A1) are polymorphic and are involved in the metabolism of tamoxifen. The CYP2D6*4 and SULT1A1*2 genotypes result in decreased enzyme activity. We therefore investigated the genotypes of CYP2D6 and SULT1A1 in 226 breast cancer patients participating in a trial of adjuvant tamoxifen treatment in order to validate the benefit from the therapy.


The patients were genotyped using PCR followed by cleavage with restriction enzymes.


Carriers of the CYP2D6*4 allele demonstrated a decreased risk of recurrence when treated with tamoxifen (relative risk = 0.28, 95% confidence interval = 0.11–0.74, P = 0.0089). A similar pattern was seen among the SULT1A1*1 homozygotes (relative risk = 0.48, 95% confidence interval = 0.21–1.12, P = 0.074). The combination of CYP2D6*4 and/or SULT1A1*1/*1 genotypes comprised 60% of the patients and showed a 62% decreased risk of distant recurrence with tamoxifen (relative risk = 0.38, 95% confidence interval = 0.19–0.74, P = 0.0041).


The present study suggests that genotype of metabolic enzymes might be useful as a guide for adjuvant endocrine treatment of postmenopausal breast cancer patients. However, results are in contradiction to prior hypotheses and the present sample size is relatively small. Findings therefore need to be confirmed in a larger cohort.

Place, publisher, year, edition, pages
2005. Vol. 7, no 3, R284-R290 p.
Keyword [en]
breast cancer, CYP2D6, polymorphism, SULT1A1, tamoxifen
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-14534DOI: 10.1186/bcr993OAI: diva2:23662
Original Publication: Pia Wegman, Linda Vainikka, Olle Stål, Bo Nordenskjöld, Lambert Skoog, Lars-Erik Rutqvist and Sten Wingren, Genotype of metabolic enzymes and the benefit of tamoxifen in postmenopausal breast cancer patients, 2005, Breast Cancer Research, (7), R284-290. Licensed by: CURRENT SCIENCE LTD Available from: 2009-02-22 Created: 2009-02-22 Last updated: 2009-06-08Bibliographically approved
In thesis
1. Studies of tamoxifen resistance in breast cancer
Open this publication in new window or tab >>Studies of tamoxifen resistance in breast cancer
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oestrogen is one of the most important hormonal regulators and is known to play a key role in the development and growth of breast cancer. The majority of tumours have a hormone dependent growth, and this is indicated by the presence of oestrogen receptors (ERs). About two thirds of breast cancers occur after the menopause when the ovaries have ceased to produce oestrogen and despite the low levels of circulating oestrogen’s the tumour concentrations of oestrone, oestradiol and their sulfates have been shown to be significant. Patients with hormone dependent tumours are candidates for treatment with the anti-oestrogen tamoxifen, which acts by competing with oestrogen for binding to the ER thereby, diminish the transcription of oestrogen regulated genes. The drug is mainly metabolised by cytochrome P450 enzymes in the liver and to a lesser extent locally in the breast, where upon several produced metabolites have higher affinity for the ER than the mother substance. Patients treated with tamoxifen have in general a prolonged disease-free survival. Even if most patients respond well to tamoxifen about 30-50 % either fail to respond or become resistant by incompletely understood mechanisms. Therefore, the aim of this thesis was to investigate possible mechanisms responsible for tamoxifen resistance. In paper I and II we studied genetic variants of enzymes participating in the metabolism of tamoxifen and assessed whether these variants correlated to breast cancer prognosis and/or to the benefit of tamoxifen. The results indicate an influence of CYP2D6, CYP3A5, and SULT1A1 genotypes in tamoxifen response. Further, tamoxifen has shown to compete with oestrogen for the binding to ER. In paper III we measured the expression levels of enzymes involved in the local synthesis of oestrogens in order to see if they correlated to clinical outcome. The protein expression of stromal aromatase was shown to have a prognostic significance, especially in ER-positive patients. Finally, tamoxifen and its ER-active metabolites have shown to induce both cell cycle arrest and apoptosis and one central mediator in these processes is the tumour suppressor protein p53. The proapoptotic activity of p53 is dependent on a proline rich domain containing a common Pro-to-Arg polymorphism. In paper IV we examined the value of this genetic variant as a predictive marker for anti-cancer therapy and found that patients carrying the Pro-allele might be good responders of tamoxifen therapy. The present thesis further indicates the complexity of the mechanisms underlying tamoxifen resistance. In summary, genetic variants of metabolic enzymes, genetic variants in p53, as well as expression levels of enzymes involved in local oestrogen synthesis, may have influence on breast cancer prognosis and may be useful markers in the prediction of tamoxifen response.

Place, publisher, year, edition, pages
Institutionen för biomedicin och kirurgi, 2007. 68 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 987
Breast cancer, tamoxifen, polymorphism, metabolic enzymes, oestrogen synthesis
National Category
Cancer and Oncology
urn:nbn:se:liu:diva-8943 (URN)978-91-85715-71-8 (ISBN)
Public defence
2007-03-30, Eken, Campus US, Linköpings Universitet, Linköping, 09:00 (English)
Available from: 2007-06-01 Created: 2007-06-01 Last updated: 2009-05-11

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