Novel genetic profiling tests of breast cancer tissue have been shown to be prognostic for overall survival and predictive of local and distant rates of recurrence in breast cancer patients. One of these tests, Oncotype DXtrade mark, is a diagnostic test comprised of a 21-gene assay applied to paraffin-embedded breast cancer tissue, which allows physicians to predict subgroups of hormone-receptor-positive, node-negative patients who may benefit from hormonal therapy alone or require adjuvant chemotherapy to attain the best survival outcome. The results of the assay are converted to a recurrence score (0-100) that has been found to be predictive of 10- and 15-year local and distant recurrence in node-negative, estrogen-receptor-positive breast cancer patients. Previous studies have shown that patients with high recurrence scores benefit from adjuvant chemotherapy, whereas patients with low recurrence scores do not. To evaluate the ability to guide treatment decisions in the group with a mid-range recurrence score, the North American Cooperative Groups developed the Trial Assessing IndiviuaLized Options for Treatment for breast cancer, a randomized trial of chemotherapy followed by hormonal therapy versus hormonal therapy alone on invasive disease-free survival-ductal carcinoma in situ (IDFS-DCIS) survival in women with node-negative, estrogen-receptor-positive breast cancer with a recurrence score of 11-25. The study was initiated in May 2006 and approximately 4500 patients will be randomized. This article describes the rationale, methodology, statistical ana-lysis and implications of the results on clinical practice.