Microscopic pulmonary tumor embolism is difficult to diagnose. Herein is presented the case of a patient who suffered from acute dyspnea and breast cancer on the right side. Two weeks after the breast cancer diagnosis the patient began to experience dyspnea. After 2 weeks of dyspnea, the patient died without an accurate diagnosis of dyspnea. Autopsy indicated massive microscopic pulmonary emboli of the breast cancer. Immunohistochemistry showed that most of the cancer cells in the primary site were negative for estrogen receptors, progesterone receptors Her2/neu oncogene (triple negative), and stem cell-like markers (OCT3/4, NANOG2, CD44, CD24, aldehyde dehydrogenase 1 (ALDH1)). The breast cancer cells in the lung (the metastasized site), however, were triple negative, but were enriched in stem cell-like markers (OCT3/4(+), NANOG2(+), CD44(+)/CD24(-/low), ALDH1(+)). This is a significant case report indicating that vascular emboli themselves contain the essential molecular signature of 'stemness' independent of the origin.