Immunohistochemistry (staining particular cell types using antibodies against surface proteins) can detect plasma cells that express immunoglobulin in the cytoplasm and occasionally on the cell surface; myeloma cells are often CD56, CD38, CD138, and CD319 positive and CD19, CD20, and CD45 negative. Flow cytometry is often used to establish the clonal nature of the plasma cells, which will generally express only kappa or lambda light chain. Cytogenetics may also be performed in myeloma for prognostic purposes, including a myeloma-specific fluorescent in situ hybridization and virtual karyotype. The plasma cells seen in multiple myeloma have several possible morphologies. First, they could have the appearance of a normal plasma cell, a large cell two or three times the size of a peripheral lymphocyte. Because they are actively producing antibodies, the Golgi apparatus typically produces a light-colored area adjacent to the nucleus, called a perinuclear halo. The single nucleus (with inside a single nucleolus with vesicular nuclear chromatin) is eccentric, displaced by an abundant cytoplasm. Other common morphologies seen, but which are not usual in normal plasma cells, include:

Bizarre cells, which are multinucleated
Mott cells, containing multiple clustered cytoplasmic droplets or other inclusions (sometimes confused with auer rods, commonly seen in myeloid blasts)
Flame cells, having a fiery red cytoplasmHistorically, the CD138 has been used to isolate myeloma cells for diagnostic purposes. However, this antigen disappears rapidly ex vivo.
Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, anemia, kidney dysfunction, and infections may occur. Complications may include amyloidosis.The cause of multiple myeloma is unknown. Risk factors include obesity, radiation exposure, family history, and certain chemicals. Multiple myeloma may develop from monoclonal gammopathy of undetermined significance that progresses to smoldering myeloma. The abnormal plasma cells produce abnormal antibodies, which can cause kidney problems and overly thick blood. The plasma cells can also form a mass in the bone marrow or soft tissue. When one tumor is present, it is called a plasmacytoma; more than one is called multiple myeloma. Multiple myeloma is diagnosed based on blood or urine tests finding abnormal antibodies, bone marrow biopsy finding cancerous plasma cells, and medical imaging finding bone lesions. Another common finding is high blood calcium levels.Multiple myeloma is considered treatable, but generally incurable. Remissions may be brought about with steroids, chemotherapy, targeted therapy, and stem cell transplant. Bisphosphonates and radiation therapy are sometimes used to reduce pain from bone lesions.Globally, multiple myeloma affected 488,000 people and resulted in 101,100 deaths in 2015. In the United States, it develops in 6.5 per 100,000 people per year and 0.7% of people are affected at some point in their lives. It usually occurs around the age of 60 and is more common in men than women.