Which tumor marker is specifically used to diagnose multiple myeloma?

The tumor marker specifically used to diagnose multiple myeloma is immunoglobulins. In multiple myeloma, abnormal plasma cells produce excessive amounts of a particular type of immunoglobulin, often referred to as monoclonal immunoglobulins or M proteins. These proteins can be detected in the blood and urine, and their presence is a key indicator of the disease. Elevated levels of these proteins help confirm a diagnosis of multiple myeloma and can also be used to monitor the disease's progression or response to treatment.

The other markers do not relate to multiple myeloma in a diagnostic context. For instance, the BCR-ABL fusion gene is primarily associated with chronic myelogenous leukemia and has no role in diagnosing multiple myeloma. Chromogranin A (CgA) is used as a marker for neuroendocrine tumors, and carcinoembryonic antigen (CEA) is utilized mainly in colorectal cancer and other malignancies. Thus, immunoglobulins stand out as the critical marker for diagnosing multiple myeloma.