At present tamoxifen remains the ‘gold standard’ adjuvant hormone therapy for early stage breast cancer in both pre and post menopausal women. The use of aromatase inhibitors is at the discretion of the specialist. All three aromatase inhibitors have now been licensed for use for early stage breast cancer and preliminary recommendations from NICE are in favour of aromatase inhibitors being used as part of adjuvant therapy.
Results from the studies that have reported, have been very encouraging and aromatase inhibitors are starting to be incorporated into standard adjuvant treatment for post menopausal women with hormone receptor positive breast cancer. Opinion varies about the best way of integrating these drugs into routine use.
The most recent ASCO Technology assessment on the use of aromatase inhibitors as adjuvant therapy for postmenopausal women with hormone receptor positive breast cancer states:
General opinion following the results so far from trials looking at the use of aromatase inhibitors of early stage breast cancer is that they should become part of standard treatment. The question is how, and what implications might that have for patients, and the health service. There are likely to be particular subgroups of patients who might benefit from earlier use of aromatase inhibitors (10).
Previous studies have indicated that HER2 status may be a predictor for response to tamoxifen. A study using letrozole and tamoxifen in the neoadjuvant setting, suggested that an ER positive tumour which also expresses HER 2 may not benefit from tamoxifen therapy but may respond better to treatment with an aromatase inhibitor (12). The IMPACT trial also suggested a better response rate with an aromatase inhibitor for HER2 positive breast cancer (13).
A subgroup analysis of the ATAC trial looked at tumours which were ER+/ PR+ and compared them with tumours which were ER+/PR-. There was a significant difference in breast cancer event occurrence in favour of anastrozole in ER+/PR- tumours. However this is not supported by the BIG 1-98 or IES data. Recent data shows that patients with tumours low in ER may do better with an aromatase inhibitor as these women have greater early rates of relapse.