Hormonal Therapy - Day 31

Last night I finished my first bottle of tamoxifen, which means I've been taking it for 30 days. Only 59 bottles to go! It's probably better not to think about it that way for a while. 

What is nice to think about is that so far I have had no appreciable side effects. It's too soon to say that I won't ever experience tamoxifen side effects - based on anecdotal evidence, it seems that many women don't start experiencing side effects for a few months or more after starting the drug. But others start right away, so at least I'm not in that group. I've been trying to exercise as much as I can (not always an easy feat now that I'm back at work full time), which Dr. Hurvitz says is the best way to stave off some of the more common side effects, such as bone density loss and mood swings - but to be honest, as with so many parts of this journey, I think a lot of it is just luck. I hope my luck continues to hold as more and more of this drug builds up in my system.

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In its simplest form, the explanation of how tamoxifen works is very straightforward: ER+ breast cancers need estrogen to grow, and tamoxifen attaches to the hormone receptor in the cancer cell, blocking estrogen from attaching to the receptor and slowing or even stopping the growth of the tumor by preventing the cancer cells from getting the hormones they need. Because it prevents cancerous cells from dividing but does not cause cell death, tamoxifen is considered cytostatic rather than cytotoxic, like chemotherapy.  

Interestingly, tamoxifen itself is a prodrug, meaning it is pharmacologically inactive - it has relatively little affinity for its target protein, the estrogen receptor. However, it is transformed by the liver into active metabolites which have 30-100 times more affinity with the estrogen receptor than tamoxifen itself. These active metabolites compete with estrogen in the body for binding to the estrogen receptor. In breast tissue, some metabolites also act as estrogen receptor antagonists so that transcription of estrogen-responsive genes is inhibited. 

Tamoxifen has been used for over 40 years to treat ER+ breast cancers. Global sales of tamoxifen in 2001 were $1.024 million. Since the expiration of the patent in 2002, it is now widely available as an inexpensive generic drug. As of 2004, tamoxifen was the world's largest selling hormonal drug for the treatment of breast cancer. It is on the World Health Organization's List of Essential Medicines, a list of the most important medications needed in a basic health system.

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Until recently, most women who received adjuvant endocrine therapy to reduce the chance of recurrence took tamoxifen every day for five years. However, with the advent of newer hormone therapies, additional approaches to hormone therapy have become common. For example, some women take an aromatase inhibitor with ovarian suppression for five years instead of tamoxifen (this was Dr. Hurvitz's original recommendation for me, which I rejected due to my discomfort with the idea of ovarian suppression). Other women receive additional treatment with an aromatase inhibitor after five years of tamoxifen. Finally, some women switch to an aromatase inhibitor after two or three years of tamoxifen, for a total of five or more years of hormone therapy. 

Although I haven't called her on it yet, I'm fully expecting Dr. Hurvitz to recommend additional hormone therapy once I reach the end of my first five years. But who knows - in five years, more studies will be done, new testing may be available, new drugs could be discovered - and the standard of care could be completely different than it is today. So I'm not going to worry about it now. For now, I'm trying to focus on the satisfaction of tossing that little white bottle into the trash every 30 days.