The drug continues to have this benefiteven after you stop taking it.
In contrast to its anti-estrogen effects on breast tissue, tamoxifen has estrogen-like effects on bone.
Therefore tamoxifen (as well as Evista) may help slow or stop bone loss.
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Tamoxifen may also lower cholesterol levels, specifically LDL cholesterol.
This is true even with very small, node-negative tumors.
How It Works
Estrogen receptor-positive breast cancer cells are fed byestrogen.
Tamoxifen binds to this receptor, essentially starving the cancer cells.
Tamoxifen is broken down into a metabolite called endoxifen by the cytochrome P450 enzyme CYP2D6.
(There are also other enzymes such as CYP3A4, but CYP2D6 is likely most significant.)
Anything that reduces the activity of CYP2D6 can result in a reduced amount of the active metabolite.
A review of studies found that extensive metabolizers appear to have better outcomes than poor metabolizers.
In other words, you probably won’t know if this issue applies to you.
After menopause, the conversion of other hormones into estrogen is the primary source of estrogen.
Aromatase inhibitors work by blocking this conversion, hence reducing estrogen levels.
Common side effects of tamoxifen include:
Hot flashes are actually linked with better survival from breast cancer.
Risks
Tamoxifen’s actions on endometrial tissue can raise the risk ofuterine cancer.
The risk is highest for postmenopausal women, but it is still rare.
In particular, several antidepressants, as well as over-the-counter allergy medications, may reduce the effectiveness of tamoxifen.
This reduction in breast cancer recurrence must be weighed against potential side effects for each person.
A Word From Verywell
Tamoxifen can be a lifesaver for some women with breast cancer.
As with all medications, however, there are potential risks and side effects.
Frequently Asked Questions
No, tamoxifen is not chemotherapy.
Side effects, such as hot flashes, can start pretty quickly after starting tamoxifen.
Some side effects, such as improving bone density, can take some time to be noticed.
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