This is group of drugs with abilities to block an enzyme called aromatase, which is responsible form production of small amounts of estrogen in post-menopausal women whose ovaries are no longer functioning. A group of drugs called aromatase inhibitors work by blocking this enzyme thus decreasing its level in post-menopausal women. Estrogen production in pre-menopausal women do not depend on aromatase enzyme hence these groups or drugs are not effective in pre-menopausal women. Three drugs of this group are approved for use in treating breast cancer. These are letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin). Aromatase inhibitors are often the drugs of choice in post-menopausal women with hormone receptor positive tumor who had breast cancer recurrence. Recent studies have shown that anastrozole (Arimidex) can be used for adjuvant therapy of breast cancer in place of tamoxifen in post-menopausal women. The risk of uterus cancer and blood clots are much less with the use of anastrozole compared to tamoxifen and it is probably more effective in preventing the breast cancer recurrence. The risk of osteoporosis and fracture are
however higher with anastrozole compared to tamoxifen. Removal of all the post-menopausal estrogen may be responsible for the increased risk of osteoporosis and fracture. The experience with tamoxifen spans to the last twenty years, whereas our experience with anastrozole is limited to the last few years. These are some of the factors we should consider before choosing between tamoxifen and anastrozole as the choice of adjuvant therapy. A recent study has shown that in the setting of adjuvant therapy, at the end of five years of tamoxifen if the treatment is continued with letrozole that would give further benefit for prevention of breast cancer recurrence in post-menopausal women. Another recent study has shown that after about 30 months of tamoxifen, if the treatment is switched to exemestane that would give better results than continuing with tamoxifen for five years in post-menopausal patients. As you may notice by reading the above information that the aromatase inhibitors are really coming to the front line of treatment and in the next few years they are expected to become the primary hormonal treatment of breast cancer.