Solitary plasmacytoma is a rare condition that is similar to multiple myeloma. However, it describes a single, solid mass of abnormal plasma cells in the bone or soft tissue. People who receive a diagnosis of solitary plasmacytoma may go on to develop multiple myeloma.

Solitary plasmacytoma refers to a single abnormal mass, or tumor, that consists of plasma cells, known as a plasmacytoma. Plasma cells are a type of white blood cell that has an important role in immunity.

A plasmacytoma may progress into multiple myeloma. This is another type of cancer that affects white blood cells. Some people may also describe solitary plasmacytoma as a subdivision of multiple myeloma.

The name solitary plasmacytoma derives from the fact that instead of multiple tumors in different locations, like in multiple myeloma, there is only one tumor. Many doctors believe that solitary plasmacytoma is an early, isolated form of multiple myeloma. As many people with solitary plasmacytoma may develop multiple myeloma, it is important to watch closely for signs of multiple myeloma.

There are two main types of solitary plasmacytoma: Solitary bone plasmacytoma (SBP) and solitary extramedullary plasmacytoma (SEP). These terms describe whether the clump of abnormal plasma cells occurs in the bone or soft tissue.

In this article, we will discuss solitary plasmacytoma, including its potential causes, treatments, and prognosis.

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As a 2021 article explains, researchers distinguish plasmacytoma as an intermediate stage between the earlier monoclonal gammopathy of undetermined significance (MGUS) and the later multiple myeloma.

Some experts describe these terms as different phases of the same condition, which involves plasma cells growing in an unusual, uncontrolled fashion. However, one important difference between MGUS and plasmacytoma is that the former is always asymptomatic.

At present, there is no known cause of solitary plasmacytoma. However, some evidence indicates that factors such as genetics, viral infections, and inhaled irritants may contribute.

Potential risk factors for the condition include older age, being male, and being African American. The average age at which people develop symptoms is 55–60 years, and the rate of incidence is significantly higher in individuals over the age of 60.

Incidence rates may be 2–3 times higher in males than females. Some evidence also suggests that incidence is 30% higher in African Americans than in Caucasians, and Asian individuals have a 50% lower lifetime risk of the condition. There may also be a higher risk for those with a family history of the condition.

Signs and symptoms of solitary plasmacytoma can vary slightly depending on the location of the mass of abnormal cells. Typically, a person may notice signs of pain due to compression or enlargement of the tissue the plasmacytoma is affecting.

A 2020 paper notes that common symptoms of solitary plasmacytoma may include:

  • local pain
  • spinal cord compression
  • swelling
  • pathologic bone fracture

Improvements in diagnostic techniques have helped clinicians to identify solitary plasmacytoma. At present, tools that can aid in the detection of this condition include:

  • laboratory analyses of bodily fluids
  • biopsies, which involve removing small amounts of tissue for analysis
  • imaging studies, which can help doctors to locate the presence of plasmacytomas

Using these results and comparing them to diagnostic criteria can help doctors determine the extent of the condition. Furthermore, tests such as a bone marrow aspiration and imaging tests can help identify the risk of progression or presence of multiple plasmacytomas that may indicate multiple myeloma.

The standard form of treatment for solitary plasmacytoma is radiation therapy. This involves focusing radiation, similar to X-rays, on the plasmacytoma to kill the abnormal cells. These cells are highly sensitive to radiation, and as they are localized masses, it is easier to target them with this type of treatment. Doctors may be able to achieve an 80% control rate by using radiation therapy.

Other treatment options for solitary plasmacytoma include surgery or chemotherapy. Surgery may involve complete or partial tumor removal and can help treat pathological fractures, lesions at risk of fracture, and neurological complications. More research is necessary to determine the effectiveness of chemotherapy for solitary plasmacytoma, but it may help individuals with persistent disease.

As long as no other plasmacytomas are present later on, the outlook for the condition is usually good. However, roughly 70% of people with solitary plasmacytoma may go on to eventually develop multiple myeloma. This typically occurs within 2–3 years, so it is important to closely monitor individuals for signs of multiple myeloma.

Individuals with SBP may be at a higher risk of progressing to multiple myeloma than those with SEP. However, some evidence suggests that overall survival rates for SBP and SEP may not be significantly different.

A 2019 retrospective analysis of solitary plasmacytoma cases in the United Kingdom and Brazil suggests a 5-year survival rate of almost 91%.

Solitary plasmacytoma refers to a single mass of abnormal plasma cells that can occur in bone or soft tissue. Health experts usually consider solitary plasmacytoma as an early form of multiple myeloma. As this condition may develop into multiple myeloma, it is important to closely monitor the condition.

There is still no known cause of solitary plasmacytoma. Symptoms typically include local pain, and doctors can perform tests to detect the abnormal mass. Treatment will usually involve radiation therapy. As long as no other plasmacytomas are present, the outlook is generally positive.