- Objective: To analyze the implementation of a switching policy of adjuvant aromatase inhibitor (AI) therapy sequentially after tamoxifen in consecutively treated stage I (T1N0M0) hormone receptor (HR)-positive breast cancer (BC) patients. Methods: The records of 279 consecutive HR-positive BC patients diagnosed between 2002 and 2006 and followed at the Soroka Medical Center were reviewed. Results: Two-hundred-seventeen patients who initially received tamoxifen were suitable for switching and 28 received an AI as initial adjuvant treatment. The switch was accomplished in 82.5% of the 217 patients. Those who switched to an AI had a higher proportion of T1c stage than patients eligible who were not switched, but did not differ in age, histologic grade, or having received chemotherapy. Of the 179 patients who switched, 155 (86.6%) completed at least 4.5-5 years of adjuvant tamoxifen/AI therapy. Eighteen patients discontinued AI therapy prematurely because of toxicity. Conclusions: In this stage I BC population, despite the toxicities of AI therapy, >84% of eligible patients received an AI as adjuvant therapy. Measures to improve the management of AI toxicity, such as changing to a different AI, may reduce early stopping.