During the summer of 2009, my onc suggested/recommended/insisted that I switch antidepressants because there was some research that showed that the type of antidepressant I was taking might affect the functioning of the Tamoxifen, which is supposed to prevent cancer from coming back. Here's a post I wrote about that.
So I tried several of the antidepressants that were supposed to be better for women on Tamoxifen, and none of them worked. In fact, about a year ago, I was feeling pretty crappy. Here's a post I wrote at that time.
Ultimately, I got off the new antidepressant, off the ovarian suppression study, and back onto my old antidepressant (that I know works for me). Here's a link to that post.
I thought I wrote more about it on the blog, but I guess I didn't. During that time, I read a whole lot of research about the connection between Tamoxifen and something called CYP2D6, which is an enzyme in your liver. Supposedly some people metabolize Tamoxifen differently, and this can impact how well the Tamox works to prevent future cancers. Some women took this research to heart, and had the CYP2D6 test and based their decision whether to take Tamox or not on that result. My onc wasn't convinced, so I didn't have that test. That was fine with me, because I wasn't convinced either.
Then, someone looked at antidepressants, which also are affected by the CYP2D6 enzyme in the liver, and decided to look at whether women who take certain antidepressants and Tamoxifen are more likely to have a recurrence. However, reading the research, I wasn't convinced. They were using data sets from health care corporations, with records based on women filling their prescriptions.
I looked at everything I could get my hands on, and decided, based on what I read and how I felt that I had to have good quality of life, and that was more important than a possibly reduction in efficacy of the Tamox.
So today, here's some news from a large breast cancer research conference (the San Antonio Breast Cancer Symposium):
The CYP2D6 test, also called the “tamoxifen resistance” test examines a gene called 2D6, which produces the enzyme CYP2D6. This enzyme is necessary for the body to metabolize a number of drugs, including tamoxifen. Tamoxifen has to be metabolized to endoxifen in order to work. This is done in the body by enzymes. Some people have variations in these genes that result in them making less endoxifen, and there has been some data suggesting that these people don’t do as well when they take tamoxifen. This was noted at the 2007 San Antonio Breast Cancer Symposium, when researchers presented data that showed that women who inherited a certain variation of the 2D6 gene were almost twice as likely to have their breast cancer recur, even though they were more likely to complete their tamoxifen treatment.So, as usual, I'm both relieved, and angry. Relieved because I really didn't believe the initial research that showed that the antidepressants impacted the Tamoxifen. Angry because lots of women went ahead and changed their antidepressant because of this research. Also, some women took the CYP2D6 test to see how they "metabolized" Tamoxifen and made treatment decisions based on this test. So now what do they do?
To explore this question further, researchers took advantage of two large studies that were done to look at the benefit of tamoxifen versus an aromatase inhibitor (which is metabolized differently, and is not affected by CYP2D6). Their findings refuted the previous data, showing that the presence of common mutations in the genes that control the enzymes that metabolize tamoxifen did not have an effect on whether women were likely to have a recurrence. They also found that antidepressants that are thought to inhibit CYP2D6 actually had no effect on whether women taking tamoxifen had a recurrence. In sum, the researchers concluded that for postmenopausal patients with hormone-sensitive early breast cancer, CYP2D6 testing is not justified to determine whether to give tamoxifen. They also found that, in contrast to what has been suggested, the presence or absence of hot flashes should not be used as an indicator of whether tamoxifen is effective. (link back to original article by Dr. Susan Love)
This breast cancer business is a moving target. You try to make decisions based on the latest information, but next year, it might change. Argh!