Background: Plasma cell mastitis (PCM), also known as mammary duct ectasia, is a chronic nonbacterial breast inflammation characterized by duct expansion and plasma cell infiltration. The severe and intense clinical manifestations profoundly affect the quality of life of female patients. Although the pathological process of PCM is known to include four stages (duct dilatation, inflammation, abscess and fistula), there is still lack of imaging techniques and serum markers with high specificity in clinical practice. Due to recurrent acute attacks and the prolonged healing process of the disease, most patients choose to accept mastectomy. Summary: We searched for studies, reports and reviews referring to PCM in the past 20 years; more than half of the results were related to animal studies, and little attention has been paid to human beings, which may explain the frequent misdiagnosis of PCM as breast cancer and the limited treatment options. This review focuses on the current diagnostic methods and markers for PCM and hierarchically discusses the typical clinical features, etiological causes and relevant molecular mechanisms of PCM. Key Messages: We herein highlight the urgent need to develop more specific and sensitive biomarkers in the clinical laboratory. It will help to establish a standardized flowchart for the diagnosis and treatment of PCM in order to improve recovery for female patients.