Femara (letrozole) is an aromatase inhibitor that works by suppressing the production of estrogen. In postmenopausal women estrogen is still produced in the body by the adrenal gland. Decreasing this production is a way of decreasing the risk of recurrence.

Tamoxifen on the other hand works by blocking the estrogen receptors on the cancer cell itself resulting in slower growth of the cell or cell death. Tamoxifen can be given to post or premenopausal women but Femara would only be prescribed to women that are postmenopausal. The reason being, is that a premenopausal women will still have estrogen produced by the ovaries. Femara would not be effective in this instance.

A Phase III clinical trial that is ongoing shows preliminary results that Femara is superior than Tamoxifen in women with early stage disease that are postmenopausal. The results of the study were published in the Annals of Oncology.

The study includes a little over 8,000 postmenopausal women with hormone receptor early breast cancer. The women were placed in one of four groups.

• Five years of Tamoxifen
• Five years of Femara
• Two years of Tamoxifen followed by three years of Femara
• Two years of Femara followed by three years of Tamoxifen

The preliminary results of the study show that -- A benefit of Femara over Tamoxifen was observed in most subgroups of women, but there was a suggestion that Femara may provide greater than average reduction in risk among women with poor prognostic factors (four or more involved lymph nodes, tumor larger than 2 cm, and vascular invasion).

Take home message -- If you are a postmenopausal women diagnosed with estrogen positive early breast cancer you may want to ask your doctor about starting on an aromatase inhibitor instead of Tamoxifen for first line treatment.