In the United States, more than 3 million women are living after a breast cancer diagnosis. There is great need for additional breast cancer adjuvant treatments that are low-cost and low toxicity. These would not only save thousands of lives, but offer improved quality of life for those who do not tolerate current treatments, and treatment options to women in developing countries who currently get none. We will enroll 3000 women with node-positive HER2 negative Stage II or III breast cancer with a 11 randomization to aspirin 300 mg daily versus placebo. Primary endpoint is invasive disease-free survival including local and distant. Secondary endpoints include recurrence-free interval local and distant, overall survival, cardiovascular disease, toxicity, and adherence. We will exclude those at high risk of bleeding complications with aspirin greater than or equal to age 70, history of prior stroke, significant gastrointestinal bleeding, anticoagulation or those with indications for taking aspirin history of myocardial infarction or atrial fibrillation Breast cancer advocates will be involved in the creation of all recruitment letters, consent forms, and information sheets. We would conduct the trial in a multi-center collaboration of the Brigham and Womens Hospital, Dana Farber Harvard Cancer Institute, and the Alliance for Clinical Trials in Oncology. The research infrastructure, long-standing leadership roles in clinical trials, and ability to rapidly accrue subjects make the assembled research team ideal to lead a US trial within the proposed time frame.