Formestane, a steroidal aromatase inhibitor after failure of non-steroidalaromatase inhibitors (anastrozole and letrozole): Is a clinical benefit still achievable?

Background: There are few clinical data on the sequential use of aromatase inhibitors (AI). This paper focuses on the relevance of clinical benefit CB (CR + PR + SD greater than or equal to6 months) in postmenopausal metastat ic breast cancer (MBC) patients treated with the steroidal aromatase inhibi tor (SAI) formestane (FOR), who had already received non-steroidal aromatas e inhibitor (nSAI): letrozole (LTZ) or anastrozole (ANZ). Patients and methods: Twenty postmenopausal women with MBC were analysed in this retrospective two-centre study with the sequence nSAI-FOR. When recei ving ANZ, 1 of 11 achieved a complete response and 9 of 11 a stable disease greater than or equal to6 months, and receiving LTZ 1 of 9 achieved a part ial response and 4 of 9 a stable disease greater than or equal to6 months. The analysis of the entire population treated with FOR showed an overall CB of 55% (11 of 20) with a median duration of 15 months and median time to p rogression (TTP) of 6 months. Conclusions: Formestane 250 mg once bi-weekly seems to be an attractive alt ernative third-line hormonal therapy for the treatment of patients with MBC , previously treated with nSAI.