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Tamoxifen CYP2D6 Pharmacogenetic Testing
(for phycisians only)
What?
- CYP2D6 pharmacogenetic testing for tamoxifen patients
We offer:
1. CYP2D6 pharmacogenetic testing for patients taking tamoxifen.
Why?
- Impaired CYP2D6 function, by whatever means, can make tamoxifen less effective
Tamoxifen is converted to its more potent active metabolite, endoxifen via hepatic CYP2D6 metabolism. Many patients have impaired CYP2D6 function, either by genetic predisposition or by ingesting medications or herbals which act as CYP2D6 enzyme inhibitors.
Patients with inadequate conversion of tamoxifen to endoxifen, by whatever means, will not receive the maximal therapeutic benefit that tamoxifen is known to provide.
Recent studies have shown that CYP2D6 metabolic activity is an independent predictor of breast cancer outcomes in women with estrogen receptor positive breast cancer treated with tamoxifen. (Goetz et al, 2007)
Patients with decreased CYP2D6 metabolic activity, whether caused by genetic or environmental inhibition, or both, showed significantly shorter time to recurrence and worse relapse-free survival than patients with 'normal' 2D6 metabolism.
Five to ten percent (5-10%) of all Caucasian women are classified as poor metabolizers of CYP2D6 metabolized medication, such as tamoxifen.
Intermediate metabolizers and even extensive metabolizers can have their CYP2D6 metabolic activity reduced by the concomitant use of CYP2D6 inhibitors.
When?
- At what time should patients be genotyped for their CYP2D6 profile
Ideally a patient's CYP2D6 genotype will be tested prior to or coincidental with the initiation of tamoxifen therapy for breast cancer. Patients already receiving tamoxifen therapy can also be tested at any point.
For patients started on tamoxifen, all current medications (prescription, OTC and herbals) should be screened for CYP2D6 inhibitory activity. Whenever a new medication is being considered, it too should be screened for CYP2D6 inhibitory activity. This monitoring should be ongoing and continuous for the duration of tamoxifen therapy. This inhibitor monitoring service is a separate service offered by Pharmacy.ca. Click here
for more information.
How does it work?
- A simple, in-office, buccal swab collection
A test sample is collected right in your office using our proprietary buccal swab kit . The entire sample collection process takes about 5 minutes. The kit contains all the components you will need including a postage prepaid sample return envelope. There is no cost to the physician for the test kit. Pricing for the patient is below.
Once we receive the samples the processing of the assay, the genotyping, phenotyping and development of the complete written report takes about 10 days to 2 weeks. As the testing physician you will receive a written report and recommendations about the patient's CYP2D6 status.
References:
Goetz MP et. al, 2007, The impact of Cytochrome P450 2D6 metabolism in women receiving adjuvant tamoxifen, Breast Cancer Res Treat , Jan;101(1):113-21
NOTE: The contents of this page are intended for physicians and trained medical professionals.
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311 Sherbourne St, Toronto, On M5A 3Y1 1-416-960-7768 OCP Accreditation number 17533, owner is Central Medical Pharmacy Inc. Designated manager is Veronique Koo, B Sc Phm. Pharmacists are available for counselling during operating hours.
The information provided on our site is for general information purposes only and is not intended to qualify, supplement or replace that of your medical professional. Your doctor or healthcare giver should undertake diagnosing and treating your medical condition.
[c] © 1999 PurePharm Inc.
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