Hormone Therapy - Aromatase Inhibitors

In post-menopausal women, the ovaries are no longer functional and cannot produce oestrogen. Their main source of oestrogen comes from the adrenal glands and from special chemicals, called enzymes, that act on areas of the body such as fatty tissue. One of the most important of these enzymes is called aromatase.

A new group of drugs called aromatase inhibitors reduce oestrogen production in post-menopausal women by blocking the action of the aromatase enzymes. Examples of these drugs are letrozole (Femara), anastrozole (Arimidex) and exemestane (Aromasin).

These drugs are prescribed for post-menopausal women with advanced or early breast cancer containing oestrogen receptors (ER positive) . Post-menopausal women with advanced breast cancer or whose breast cancer progresses or relapses while on tamoxifen are also suitable for treatment with this type of drug, provided that the cancer contains oestrogen receptors.

These drugs are less likely than tamoxifen to cause weight gain, womb cancer or deep-vein thrombosis.

The  final results of a study comparing Arimidex with tamoxifen in postmenopausal women with early breast cancer that contains hormone receptors, suggests that Arimidex is better than tamoxifen in preventing breast cancer recurrence and has less-frequent side-effects.

Recent research has also shown that the use of aromatase inhibitors such as Aromasin or Arimidex (for 3 years) in sequence after tamoxifen (for 2 years) for early breast cancer in postmenopausal women improves outcome. Women completing 5 years of tamoxifen seem to benefit further if they take Femara for 2 years.

However, bone mineral density scans (known as Dexa scans) may be required to identify women at risk of brittle bone disease. In such cases, other drugs to protect the bone can be given in conjunction with aromatase inhibitors. Further research in this area is urgently required..

It is also likely that these drugs may be used to prevent breast cancer in high-risk women.
 
The author believes that for postmenopausal women diagnosed with low risk (node negative, smaller than 2 cm) early invasive breast cancer that contains hormone receptors, the best approach would be to take tamoxifen for 2 years and then to switch from tamoxifen to an aromatase inhibitor such as Aromasin or Arimidex for 3 years.

For postmenopausal women diagnosed with high risk (node positive, larger than 2 cm) early invasive breast cancer that contains hormone receptors, the best approach would be to take Femara for 5 years. For women completing 5 years of tamoxifen, Femara should be considered for further two years especially in node positive patients.

Vitamin D and calcium supplements and monitoring of bone density are recommended whenever aromatase inhibitors are used.