We describe the case of a 56-year old woman with no prior psychiatric history 
who was diagnosed with hormone receptor positive early-stage breast cancer and 
who developed severe mood changes after administration of anastrozole, which 
resolved after discontinuation of treatment. Aromatase inhibitors (AIs) are the 
preferred hormonal approach for postmenopausal women with estrogen hormone 
sensitive breast cancer. The third-generation agents (anastrozole, letrozole, 
and exemestane) have been shown to be more effective and safer than the 
selective estrogen receptor modulators tamoxifen and raloxifen. Treatment 
strategies with these agents include the use of an AI as an upfront strategy for 
5 years, as a sequential approach after 2-3 years of tamoxifen, or as extended 
use after the classical 5 years of tamoxifen. The side effects of AIs, as 
compared with selective estrogen receptor modulators, are different, reflecting 
the specific mechanism of action of these drugs. AIs are well tolerated and 
cause a lower incidence of gynecological symptoms (vaginal bleeding, discharge, 
and endometrial neoplasia), venous thromboembolic events, and hot flashes 
compared with tamoxifen. However, the use of AIs have been associated with loss 
of bone density, arthralgia, myalgia, a negative effect on lipid metabolism, and 
cardiovascular risk (Tomao et al., 2011). Mood disturbances, somnolence, 
anxiety, fatigue, hot flashes, and memory impairment have been reported among 
patients receiving anastrozole as adjuvant therapy.