The Pharmaceutical Journal
Vol 268 No 7185 p197-203
16 February 2002

This article
Reprint
Photocopy

News summary

Related websites
Journal of Clinical Oncology (www.jco.org)
AstraZeneca (www.astrazeneca.co.uk)

Letrozole has greater biochemical effect than anastrozole in vivo

A study has shown that letrozole (Femara) is a more potent aromatase inhibitor than anastrozole (Arimidex). However, the study did not compare the efficacy of the two drugs so any clinical relevance could not be determined.

The two drugs, which are used for the treatment of advanced breast cancer in postmenopausal women, have previously been shown to cause profound suppression of plasma oestrogen levels. The researchers comment that their clinical superiority over conventional treatment supports the hypothesis that the degree of oestrogen supression may be important for clinical outcome.

The study involved 12 postmenopausal women who had metastatic breast cancer who were treated sequentially with anastrozole 1mg followed by letrozole 2.5mg (or vice versa) each given once daily for six weeks. The researchers measured total body aromatisation as well as plasma levels of oestrone, oestradiol and oestrone sulphate before and at the end of each treatment period.

They found that in vivo aromatase inhibition was more complete after treatment with letrozole. The mean percentage inhibition while patients were treated with anastrozole was 97.3 per cent compared with more than 99.1 per cent while they were treated with letrozole (P=0.0022).

"Any correlation (or lack of such) between oestrogen suppression and clinical outcome ... would provide us with information about whether the degree of oestrogen deprivation is of clinical importance," the researchers say. Alternatively, there may be a threshold for oestrogen levels with respect to clinical response, they add (Journal of Clinical Oncology 2002;20:751).

A spokeswoman for AstraZeneca, manufacturer of Arimidex, told The Journal that the findings did not reveal a greater clinical efficacy for letrozole in advanced breast cancer patients. "The study design was such that it did not show an impact on tumour outcome in advanced breast cancer patients, but only marginal differences in oestrogen suppression," she added.