PLE-8120

The yearly mammogram of a 65-year-old postmenopausal woman shows an irregular area of microcalcification that has grown in size compared with her mammogram from 2 years ago. She missed her mammogram last year. Physical examination is unrevealing, without lymphadenopathy or nodularity in the breasts. You refer her to a surgeon, and a 2-cm invasive ductal carcinoma is removed from her left breast. Sentinel node biopsy shows two positive lymph nodes, and axillary dissection reveals five additional positive nodes. The tumor expresses the estrogen receptor (ER). Which of the following interventions would increase her chance of cure?