[Efficacy of sequential treatment with anastrozole following exemestane compared with exemestane following anastrozole in patients with metastatic breast cancer].

Background: There are three third-generation aromatase inhibitors (AI) available in Japan. Though it is supposed that they can be administered sequentially because of their little cross-resistant effect, it is not definite which sequential treatment is best.

Purpose: To examine retrospectively the difference in efficacy by the AI sequence when anastrozole ( ANA) and exemestane (EXE) are clinically administered sequentially for patients with metastatic breast cancer.

Patients: We examined 22 patients with metastatic breast cancer administered ANA alone as first-line AI treatment, EXE alone as second-line (A--> E group), and 13 patients given EXE alone as first-line AI treatment (E --> A group) since December 2002 in our hospital.

Method: In the A --> E and E --> A group, we examined overall response rate, clinical benefit (CB) rate, time to progression (TTP) for the first- and second-line treatment, respectively, overall survival (OS) after starting AI and successive efficacy of the two AIs.

Results: There were no significant differences between the two groups in patient characteristics and history of prior treatments. Overall response rate of the first-line treatment in the A--> E and the E--> A group was 31.8% and 38.5%, and the CB rate was 68.2% and 53.8%, respectively. Overall response rate of the second-line treatment in the A --> E (22 cases) and the E --> A (3 cases) group was 13.6% and 0%, and the CB rate was 36.4% and 33.3%, respectively, reflecting no particular differences. In the A --> E group, five (33.3%) among 15 cases obtained CB by EXE and three (42.6%) among 7 cases who did not obtain CB by ANA did so by EXE. Also, in the E--> A group, one among 3 cases who did not obtain CB by EXE did so by ANA. No significant differences were observed in TTP and OS between the two groups.

Conclusion: When ANA and EXE are administered sequentially, no particular difference in efficacy occurs due to the sequence. In some cases, 2 agents become effective successively, and cases resistant to first-line treatment can expect efficacy from second-line treatment. Sequential treatment with the two agents seems to provide very significant efficacy in clinical practice regardless of the order of administration.