Breast Cancer Hormone Therapy, Tamoxifen and Side Reactions
In general, medical oncologists have three toolboxes. The first toolbox, which most people are afraid of and commonly know of, is chemotherapy. The next tool box is endocrine or hormone therapy. Some breast cancers use lady hormone receptors to help themselves grow. If you can get rid of what those receptors are binding to in order to help them grow, then you can drastically harm that cancer and cut down its dividing right.
Now, in breast cancer there are generally two strategies to do that. There's a strategy, where we can bind the receptor, and when we do that, the estrogen can no longer get inside the cancer cell. And then there's a second strategy, where we can block the enzyme that turns pre-estrogen into active estrogen. And when we block that enzyme, a woman isn't really meaningfully making a whole bunch of estrogen anymore.
For a woman that's gone through menopause either of these options is fine. But for a woman, who hasn't gone through menopause, we generally go with the estrogen receptor blocking strategy. The strategy, where we get rid of the estrogen, has a serious toxicity that only happens in premenopausal women. For a premenopausal woman we use a drug, generally called Tamoxifen. That's the pill that a woman would take every day by mouth for a period of five years and that blocks the entry of the estrogen into the cancer cells.
There are two serious side effects that women hear about. The first one is blood clot. That's when you get a clot in the major vessels in the legs or in the arms. Fortunately, the rate of this happening is very low. And the study shows that it's about 2-3% overall, and it turns out mostly in those women, who happen to be obese or smoke, or have a family predisposition for blood clots. So, we can identify the patients, who are generally at higher risk for this event, and use different strategies as required.
So, the other major toxicity that really only happens in women, who've gone through menopause, is endometrial cancer. So, you're like that: “I'm taking this medicine to prevent breast cancer, and then you're going to give me endometrial cancer.” But, fortunately, there's an early warning indicator. For most women there would be some sort of dysfunctional bleeding, and if that's brought to the attention of the doctor and something can be done definitively about it at that point.
And, finally, what about aromatase inhibitors, then these are medicines that are also pills and that are taken once by mouth, and like the Tamoxifen are often prescribed for five years. But they work fundamentally different, because they deplete estrogen. They may be more effective. We've done now multiple studies, looking at this in postmenopausal women. And when these two strategies are compared head-to-head, then the strategy, where we get rid of estrogen by making it not be produced, is the better strategy. On balance, it works anywhere from 10-30% better. And now there's some evidence that it might, actually, save more lives. Finally, it turns out to be less toxic. So, that becomes the standard choice that we offer most patients, who've gone through menopause.
So, common things we might hear are about our hot flashes and night sweats. Over time some women can have a drop in their bone density. Because of that toxicity doctors are very careful about looking at bone density at various times during treatment to make sure that that's not happening. The good news though is that these medicines are just as likely, and in some cases more likely, to provide benefit than the chemotherapy. So, it shouldn't be taken lightly, when a doctor offers you an anti-estrogen therapy. It's also the good stuff, and it's worth getting through the full course of therapy that's recommended for that reason.