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Lynn65's avatar
Lynn65
Member
7 years ago

Endoxifen and CYP2D6 test

Hi, 

i’ve been reading posts for a few months since being diagnosed with early breast cancer in early November.  I really appreciate posts people make - it’s been a comfort to come and on and read the real deal. I continue to be blown away by how little I understood breast cancer and its ongoing impacts before getting it myself. I’m sorry that we are on this cancer path, but I appreciate the group support. 

I’m hormone receptor positive/her2 negative and have had sentinel node biopsy, lumpectomy and radiotherapy.  I was fortunate enough to be able to get the OncotypeDX test, which showed chemotherapy would only give 1% benefit.  Prior to test results, my oncologist was strongly recommending chemo.   I’m about to start tamoxifen.  

I usually take really low doses of medications, way below the standard dose, for anything to do with pain, migraine, or low blood pressure.  A doctor has suggested that I am a slow metaboliser for drugs processed through the liver, but I don’t really understand what that comment means.

In looking at tamoxifen, it is metabolised by the liver (best I can tell), into endoxifen which seems to be its “active ingredient”. 

Sorry if I’m repeating a question, but has anyone ever looked into testing for CYP2D6 which is the gene (I think that’s what it is) that metabolises tamoxifen.   I read some articles that say it’s all inconclusive, and others suggesting that testing is useful, as if you are a poor metaboliser, then need to look at using aromatise inhibitors earlier (with ovary function suppression?).   Testing is offered but not sure if it is bunkum.  Here’s one link where the test is described: https://www.dhm.com.au/media/21900626/pharmacogenomics_brochure_2013_web.pdf

Any thoughts?  (Even if it’s just that I’m overthinking it!)

Thanks, and warm thoughts to folk out there for a good night’s sleep tonight



6 Replies

  • I am fascinated Lynn! I'm looking forward to what you discover. Good on you for pursuing it. K xox
  • I just wanted to post an update — I went to my oncologist, who assured me that CYP2D6 is a hot topic at the moment. She said, however, that changing her treatment based on CYP2D6 wasn’t according to the standard for treatment, so she would need information on how to respond to test results .

    Fortunately, I remembered to take in international guidelines on CYP2D6 and tamoxifen therapy, and also a sample report from the testing agency. She was happy to go with it, but suggested I look at Australian Clinical Labs for their report since they were in the same building.  

    I rang and spoke to about 6 people in a round robin pass the parcel at Australian Clinical Labs.  They didn’t seem to understand that as a patient I would want to see what the sample report for a non-Medicare test would look like.  In the end, although it was $100 instead of the $197 at SonicGenetics, I went with what I could see with Sonic, their Pharmacogenetics test, which includes body’s ability to metabolise tamoxifen as well as other drugs.  

    I don’t think it is a very common test yet.  There aren’t many collection agencies for SonicGenetics around Melbourne.  They are associated with Melbourne Pathology but not all their sites collect blood for the CYP2D6 test.  I’ll get the results in about 2 weeks.   I’ll be curious to see what it says, just in general!
  • @iserbrown. Thanks for your reply- it made me smile - wryly - as I thought about the stuff that we’re all learning that we wish we didn’t know. 
  • It's a whole new lot of  terminology that we try and absorb as we go along
    Best wishes 
  • Thanks @kmakm for the welcome and the offer!  Yes, I’m in Melbourne. 

    Just in case my effort at PM’ing goes astray, I’m noting here that I’ve sent you one. 

    Thanks again 
  • Hi @Lynn65. Welcome to the forum!

    I've not heard of this at all, but then in the toss up between Tamoxifen and an AI, my oncologist said the AI had the edge and that's what I went on.

    I have however seen a private genetic counsellor about a different genetic issue, a gene mutation. He was excellent, and very experienced. Perhaps that could be a good route to explore?

    If you are in Melbourne and are interested, PM me and I can give you his details.

    Good luck, and let us know how you get on. K xox