This study aims to make clear the following aspects of breast cancer patients and their occupation. 1. What percentage of patients have changed their working status around surgery? 2. When did patients change their employment? 3. What is the cause of the employment change? We investigated 269 patients who underwent curative surgery for primary breast cancer at one university hospital in Tokyo. Patients who were under the age of 58 at the time of surgery and had the experience of being a company or government employee during a year prior to the surgery were used as sample for analysis. To determine factors related to the employment change, multiple logistic regression analysis was performed. Nineteen percent patients changed the employment status before and after surgery. Of those, 19% changed the employment by the end of surgery month while 42% did by the fourth month after surgery. Treatment-related factors such as mastectomy and the combination of chemotherapy and hormone therapy affected changes in employment. We believe that the validity of our study can be confirmed by comparing with the previous study results. We show the potential large effects of cancer treatment on patients’ daily lives.