Know Cancer

forgot password

Tamoxifen Pharmacogenomics and the Prevention of Recurrent Breast Cancer

50 Years
Not Enrolling
Breast Neoplasms, Tamoxifen

Thank you

Trial Information

Tamoxifen Pharmacogenomics and the Prevention of Recurrent Breast Cancer

Tamoxifen is a non-steroidal hormonal drug with weak estrogen agonist and potent estrogen
antagonist actions. The liver CYP450 metabolic enzyme systems are responsible for
metabolizing tamoxifen (the pro-drug form) into its active metabolites. A secondary
tamoxifen metabolite known specifically as 4-hydroxy-N-desmethyl-tamoxifen or endoxifen is
recognized as the principal potent metabolite responsible for tamoxifen suppression of
estrogen-dependent cell proliferation, the stimulus for breast tumor growth.
Biotransformation to endoxifen is through the CYPP450 2D6 pathway; therefore, the ability of
tamoxifen to effectively suppress breast cancer is jeopardized in patients with certain
CYP450 2D6 genetic variants and/or those receiving drug therapy that are known to alter
CYP450 2D6 function (i.e., with CYP450 2D6 inhibitors).

Four phenotype expressions classified as ultrarapid, extensive, intermediate and poor
metabolizers can be discerned from genotype testing for CYP450 2D6 activity. Patients with
normal metabolic activity are known as extensive metabolizers given that they possess either
two (genotype = wt/wt) or one (genotype = wt/vt) functioning CYP450 2D6 gene that converts a
sufficient amount of tamoxifen in to its active form. Intermediate metabolizers have at
least some or very low CYP450 2D6 activity and there does not appear to be uniform consensus
on the impact of this phenotype on tamoxifen drug disposition. Poor metabolizers lack any
functional CYP450 2D6 activity, and therefore, they do not metabolize tamoxifen enough to
produce sufficient endoxifen activity. Approximately 10% of patients (7% of Caucasians and
1-3% of other ethnic groups) are poor metabolizers with a complete absence of CYP450 2D6

The genetic variants associated with diminished or absent CYP450 2D6 activity are found on
CYP450 2D6 alleles *3, *4, *5, *6 and *10. The *3, *4, *5 and *6 alleles, when present in
variant form (genotype = vt/vt), account for approximately 97% of nonfunctional CYP450 2D6
variants in caucasians. Of these mutations, those in CYP450 2D6 *4 are most significant for

Poor metabolizer phenotype has been associated with worse relapse-free breast cancer
survival and increased risk (up to three times that of intermediate metabolizer status who
have some CYP450 2D6 activity) for breast cancer recurrence.

Diagnostic technology now exists to aid in determining which tamoxifen patients are
potentially receiving suboptimal treatment from existing alterations in one or more of the
approximately 80 alleles of the gene coding for the CPYP450 2D6 enzyme. Recognition of this
phenomenon provides physicians and their patients the opportunity for considering the use of
other anti-estrogen drugs such as aromatase inhibitors in women whose CYP450 2D6 phenotype
puts them at risk for poor response to tamoxifen therapy.

This study will use this diagnostic technology to determine a patient's phenotype provide
additional clinical information and alternative drug therapies to the patient's physician.

Inclusion Criteria:

- Patient currently has a pharmacy benefit with Medco for an enrolled client

- Patient has a adjudicated tamoxifen pharmacy claims within the last six months

- Patient is still taking tamoxifen to prevent recurrent breast cancer

- Patient is a natural postmenopausal women 50 years of age or older

- Patient signs consent

- Patient is willing to provide sample for genetic testing

- Physician managing tamoxifen therapy is willing to order pharmacogenetic test

Exclusion Criteria:

- Patient is male

- Patient is under 50 years old

- Patient has previous history of CYP450 2D6 testing

- Patient is no longer taking tamoxifen

- Patient refuses to sign consent

- Patient wishes to no longer participate after testing

- Patient's physician refuses to order pharmacogenetic test

Type of Study:


Study Design:

Observational Model: Cohort, Time Perspective: Prospective

Outcome Measure:

Determine the prevalence of different CYP450 2D6 phenotypes including poor metabolism status

Outcome Time Frame:

14 months

Safety Issue:


Principal Investigator

Robert Epstein, MD, MS

Investigator Role:

Principal Investigator

Investigator Affiliation:

Medco Health Solutions, Inc.


United States: Institutional Review Board

Study ID:




Start Date:

October 2007

Completion Date:

January 2009

Related Keywords:

  • Breast Neoplasms
  • Tamoxifen
  • Estrogen Antagonists
  • Antineoplastic Agents, Hormonal
  • Hormone Antagonists
  • Hormones
  • Hormone Substitutes
  • Selective Estrogen Receptor Modulators
  • Estrogen Receptor Modulators
  • Neoplasms
  • Neoplasms by Site
  • Breast Neoplasms
  • Neoplasms



Robert Epstein Franklin Lakes, New Jersey  07417