Gene Expression–Guided Adjuvant Chemotherapy in Breast Cancer

To the Editor: The Trial Assigning Individualized Options for Treatment (TAILORx) conducted by Sparano et al. (July 12 issue) 1 showed that endocrine therapy alone was noninferior to chemoendocrine therapy in women with hormone-receptor–positive, human epidermal growth factor receptor 2–negative, axillary node–negative breast cancer who had a midrange 21-gene recurrence score. Recurrence scores based on the 21-gene breast cancer assay range from 0 to 100, with high scores indicating a chemotherapy benefit and low scores indicating a low risk of recurrence in the absence of chemotherapy. The Ki-67 index, a defined biomarker of the response to treatment and clinical outcome in . . .