Monoclonal gammopathy of undetermined significance (MGUS) is a condition where an abnormal protein, known as monoclonal protein or M protein, is found in the blood. This protein is produced by a type of white blood cell called a plasma cell. MGUS is usually discovered incidentally during blood tests and does not cause any symptoms. While MGUS itself is not cancerous, it can increase the risk of developing certain blood disorders, such as multiple myeloma or Waldenström macroglobulinemia. Regular monitoring by a healthcare provider is essential to detect any changes that may indicate progression to a more serious condition.