Plasma cell disorders and myeloma terminology and classifications

Multiple myeloma, solitary plasmacytoma, smoldering myeloma, MGUS . . . what’s the difference? All of these disorders are related, but they have different symptoms, treatments, and prognoses. If you are new to the understanding of myeloma and related disease, read on to gain further perspective on the differences between these related plasma cell disorders.

Multiple myeloma
A cancer of the plasma cells in the bone, which causes the cells to multiply uncontrollably. The “multiple” in multiple myeloma indicates that there are multiple tumors in different areas of the bone(s). More than 90% of individuals diagnosed with myeloma have multiple tumors at the time of diagnosis.

Plasma cells are a type of white blood cell found within the bone marrow. They function as an important part of the immune system, playing a role in fighting infection by making antibodies. Malignant plasma cells produce large amounts of a single, abnormal antibody. The antibody made by myeloma cells is called monoclonal protein, also referred to as M-protein. M-proteins accumulate in blood and urine, potentially leading to damage to the kidneys or other organs.

In addition to the M-proteins, the growing number of plasma cells also crowds out other blood cells, including red blood cells, white blood cells, and platelets. Due to the reduced number of healthy cells, common symptoms of myeloma include anemia, excessive bleeding, and decreased capability of fighting infection. Furthermore, the myeloma tumors can cause damage and pain to bones. Most patients diagnosed with myeloma have osteolytic lesions, which are weakened spots on bones. Bone destruction can lead to increased levels of calcium in the blood. Patients with bone loss will receive treatment for high blood calcium and bisphosphonates to strengthen their bones.

Myeloma is rarely curable, but it is treatable. With the help of the MMRF and many researchers in the field, 10 new myeloma drugs have been approved in the past 10 years, in the time it typically takes to obtain 1 drug approval. The MMRF continues to investigate and fund the most promising treatments for myeloma.

Solitary (or isolated) plasmacytoma
A single group of malignant myeloma cells is termed a “solitary plasmacytoma.” This mass of cells can aggregate inside or outside of bone. Those that occur outside of bones are termed “extramedullary plasmacytomas,” and those occurring within bones are called “isolated plasmacytomas of the bone.” While isolated plasmacytomas of the bone can affect any bone, they tend to most frequently occur in the bones along the spinal column.

Plasmacytomas within the bone are normally diagnosed by a biopsy that reveals abnormal plasma cells. For diagnosis with a solitary plasmacytoma, bone imaging (X-rays, positron electron tomography [PET] scan, or magnetic resonance imaging [MRI]) will detect only a single lesion. Blood tests will show no anemia, no high calcium levels, and kidney function is normal.

Solitary plasmacytomas are rare, making up only 5% of plasma cell disorders, and are commonly treated with radiation therapy. Surgery is rarely needed. Prognosis with radiation alone is usually excellent, but there is a risk that plasmacytomas could recur and progress to myeloma. Therefore, individuals with solitary plasmacytoma will have long-term follow-up appointments to ensure that they remain in remission.

Smoldering (or asymptomatic) multiple myeloma
Smoldering multiple myeloma (SMM) is a precancerous form of myeloma that typically accounts for about 15% of newly diagnosed cases of multiple myeloma. It is diagnosed when low levels of M-protein are found in the blood and a slightly increased number of plasma cells are found in the bone marrow. While many patients with SMM are asymptomatic, others experience modest symptoms, such as mild anemia or a few small bone lesions.

Not all patients with SMM progress to myeloma, but many do. The risk of progression is about 10% each year for 5 years after diagnosis, 3% between years 5 and 10, and about 1% in subsequent years.

While historically the approach for SMM was “watchful waiting,” some studies are showing the benefit of earlier treatment, particularly for patients whose disease has genetic traits that put them at higher risk for disease progression to full-blown myeloma. Rather than waiting, early intervention has demonstrated success in preventing myeloma development. Further studies in early disease are underway; the MMRF is working diligently with leaders in the myeloma field to ensure that all patients receive the most effective treatment at every stage of their disease.

Monoclonal gammopathy of undetermined significance
When a small amount of M-protein is detected within the blood, this condition is termed “monoclonal gammopathy of undetermined significance,” or MGUS.

In fact, an individual with MGUS has only a 1%-2% chance of developing multiple myeloma. MGUS usually does not cause any problems or require treatment. Individuals with MGUS receive regular checkups to detect if their condition progresses, which may be marked by an increase in M-protein in the blood.


For more information, visit the following resources:

Leave a Reply

Your email address will not be published. Required fields are marked *