Effects of switching from anastrozole to letrozole, due to reimbursement policy, on the outcome of breast cancer therapy.

Background: Endocrine therapy is one of the standard treatments for estrogen-receptor-positive breast cancer patients. Letrozole is the only aromatase inhibitor (AI) included in Thailand's essential drug list since the change of reimbursement policy in 2008, when patients had to change their AIs (other than letrozole) to letrozole. This study aimed to prove that the efficacy of anastrozole plus letrozole is not less than anastrozole alone.

Methods: All medical records of breast cancer patients taking anastrozole between 2004 and 2013 were reviewed. Some patients were initially treated with anastrozole and then changed to letrozole (A-LTZ group), whereas the other patients were continuously treated with anastrozole until completion of therapy (ANZ group).

Results: In a total of 180 (55.9%) out of the 322 cases, anastrozole was replaced with letrozole. The mean age of patients in the ANZ group was 54.9 years and that of those in the A-LTZ group was 54.2 years. Clinical stages (1-4) of the ANZ versus A-LTZ patients were four versus four, 76 versus 116, 46 versus 46, and 16 versus 14, respectively. ANZ patients took AI monotherapy (46.5%) and switching strategy (53.5%), while A-LTZ patients took AI monotherapy (53.9%) and switching strategy (46.1%). The overall survival (OS) of A-LTZ patients was longer than that of ANZ patients. Stage 2 and 4 patients in the A-LTZ group also had better OS than those in the ANZ group, but stage 3 patients had similar OS in both groups.

Conclusion: Anastrozole can be replaced by letrozole any time during endocrine therapy. The patients taking anastrozole plus letrozole surprisingly seemed to have better OS than patients taking anastrozole alone.