Pregnancy occurring after multimodal therapy in a woman with breast cancer with a 1-year follow-up period is a relatively rare condition and has been defined as pregnancy-associated breast cancer. A patient can become pregnant after chemotherapy for breast cancer while she is on tamoxifen. However, the effects of tamoxifen on fetus and on the course of the pregnancy are still unknown. Here, we present a 39-year-old woman treated with chemotherapy and radiotherapy for bilateral breast cancer, and who became pregnant while taking tamoxifen.