The invention features methods, devices, and kits for predicting the responsiveness of a cancer patient (e.g., a breast cancer patient, such as a grade 1, 2, or 3 breast cancer patient) to anthracycline treatment by determining the expression levels of four chromosomal instability (CIN) genes including HDGF, KIAA0286, RFC4, and MSH6, collectively referred to as CIN4. Patients that have a low CIN4 score benefit from anthracycline treatment compared patients with a high CIN4 score.