Tamoxifen versus aromatase inhibitors for breast cancer prevention and treatment

A paper recently published in the journal Cancer Investigation summarizes the evidence in favor of aromatase inhibitors (that block the synthesis of estrogen) over tamoxifen (which antagonizes the estrogen receptors). As you probably already know, tamoxifen's side-effects are potentially very serious. It has come to my attention that clinicians assisting women in the prevention and treatment of breast cancer may not be aware of the evidence advanced by the authors:

"Aromatase inhibitors (AIs) have largely replaced tamoxifen as adjuvant hormonal therapy for postmenopausal women with early breast cancer. While tamoxifen is effective in reducing breast cancer recurrence and mortality, recent data indicate two peaks of early, mostly distant metastatic recurrences in patients receiving tamoxifen, and AIs have proven more effective in reducing recurrence. As distant recurrence has been associated with poorer survival and death, reduction in this type of early recurrence event may lead to improved survival over the long term. Recent data from major clinical trials are beginning to bear out this contention."

This is not the first time that evidence establishing the superiority of aromatase inhibition over tamoxifen has been presented. Consider this paper published earlier in the European Journal of Surgical Oncology in which the authors observe:

"The aromatase inhibitors (AI)...have demonstrated superior disease-free survival (DFS) over tamoxifen in several trials. As the choice of adjuvant endocrine treatment for early breast cancer (EBC) is evolving from tamoxifen to the AIs, this review compares the AIs with tamoxifen to help surgeons choose a treatment plan that provides the greatest reduction of recurrence risk for their patients."

The authors note the weight of already accumulated data:

"Trials of the AIs versus tamoxifen have established that patients benefit from longer DFS (disease-free survival), and in some cases distant DFS, after the use of an AI as initial adjuvant therapy, as switch therapy following 2–3 years of tamoxifen, or as extended adjuvant therapy following 5 years of tamoxifen."

Their conclusion carries additional significance considering that we have natural aromatase inhibitors that are equally useful in preventing excessive conversion of testosterone to estrogen in men (a common problem).

"The advantage in DFS associated with AIs over tamoxifen use should prompt physicians and patients to consider the use of an AI as the initial adjuvant endocrine therapy or, alternatively, switching patients who currently take tamoxifen to an AI for the remainder of adjuvant endocrine therapy."

Bear in mind that is but one point in the constellation of factors, including proportional steroid hormone production, metabolism, elimination and receptor function, that need to be measured with the appropriate tests to evaluate and correct the hormonal milieu for estrogen receptor stimulation.