Doctor, what are these "new" estrogens that do not cause breast cancer?

Recently there have been numerous references in the news about the new types of estrogens that do not cause an increased risk of breast cancer. While studies looking at an increased risk of breast cancer with traditional hormone replacement use still do not show a clear consensus, it is generally accepted that there may an increased, albeit small, risk of breast cancer with the use of traditional replacement hormones. Breast cancer is the most common cancer in women, and ranks as the second leading cause of cancer death in women. With good cause it ranks as probably the most feared cancer in women today. Any new estrogens which definitely does not have this potential side effect then become very desirable and popular in the eyes of the public.

One of these "new" types of compounds is actually not all that new. This compound is tamoxifen (Nolvadex), and was first approved in 1977 for use as a treatment for women with breast cancer. However, it was also just approved in 1998 for use in the prevention of breast cancer in women at high risk. Another compound in this category is raloxifen (Evista). This was approved in 1997 for the prevention of osteoporosis in post-menopausal women, and has some similar (as well as very different) actions as tamoxifen.

These compounds are called selective estrogen receptor modulators, or SERMs. Because of many women's valid concerns about breast cancers, and the fact that SERMs decrease this risk, SERMs have become more popular today as alternative choices to traditional hormone replacement. Unfortunately few things in life are as good as they initially seem, and there are some other attributes, both positive and negative, of SERMs that women are sometimes surprised to learn.

Tamoxifen has been long used as a type of chemotherapy for women with some types of breast cancer. It seems to work because it acts as an antagonist or competitor to estrogen, competing with natural estrogen for the receptor sites in breast tissue. It binds to the tissue and prevents the estrogen molecule from getting to the tissue. As mentioned earlier, this will reduce significantly a woman's chances of getting breast cancer in her future, and is the reason why it is now being recommended for prophylaxis in women with a high risk for breast cancer. Raloxifen also works in a somewhat similar manner on breast tissue, although it was first designed and utilized for the prevention of osteoporosis in women. It may also have some preventative effect in breast cancer, although its effects on the breast are not as well known as those of tamoxifen.

However, some women are dismayed to learn is that these two compounds do not help with hot flashes, and in fact will often make the hot flashes worse! Because of the mechanism of action, SERMs provide simply no help with the problems and symptoms of hot flashes. In addition, often the problems with dryness of the vagina may get worse. This is one problem for which women will have to seek other solutions if they choose to go with one of the SERMs.

SERMs do have a positive effect on bone density. Raloxifen is used to help prevent osteoporosis, and tamoxifen has some of the same effects. Raloxifen is presently FDA approved as an aid in helping to prevent osteoporosis in postmenopausal women. There is some preliminary evidence that these compounds may also have a positive effect on cardiovascular disease, although this effect is not as well studied at he present time.

The primary difference in these two compounds is in their effect on the uterus. Tamoxifen has been long known to have a deleterious effect on the uterus. Women who are on tamoxifen for breast cancer have an increased risk of cancer of the endometrium, or lining of the uterus. Women who are on tamoxifen should undergo some type of endometrial evaluation (either biopsy or vaginal ultrasound) at least annually and even sooner if they develop significant bleeding problems. Raloxifen on the other hand does not seem to have this same effect on the uterus, and seems to be quite safe when compared to tamoxifen in regards to effects on the uterus.

And the last significant risk of these compounds is the fact that they will increase the chances of blood clots in women's legs. Tamoxifen, raloxifen, and estrogen all increase the risk of blood clots in the legs or chest at about the same percentage rate.

SERMs have some very positive as well as negative effects, and should be considered as one of the possible alternatives for women making the important decision regarding taking hormone replacement therapy.