Extramedullary plasmacytoma is a plasma cell tumor that develops outside the bone marrow. These plasmacytomas commonly occur in the head and neck region, particularly in the upper respiratory and digestive tract. However, they can occur anywhere in the soft tissue of the body.

Doctors sometimes refer to extramedullary plasmacytoma (EMP) as solitary extramedullary plasmacytomas. Another name for the condition is solitary extraosseous plasmacytoma.

EMP is one of the two main types of solitary plasmacytoma that can occur in people. The other is called solitary bone plasmacytoma — in which case, the tumor develops in the bone.

Plasmacytomas are very uncommon and constitute nearly 5% of all plasma cell neoplasms or malignancies. EMPs only make up about a third of all solitary plasmacytoma cases, making them rare.

Keep reading to learn more about extramedullary plasmacytoma, including its causes, symptoms, treatment, and prognosis.

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A plasmacytoma is a type of plasma cell neoplasm, which refers to an atypical tissue mass that can lead to cancer. These masses can develop when the plasma cells grow and divide uncontrollably, leading to an accumulation of cells in the soft tissues of the body.

The plasma cells also produce an antibody called a monoclonal protein or M protein. This is an antibody that is not useful in the body and does not help fight infection.

In EMP, a single plasma cell tumor grows in the soft tissue, mainly in the head and neck region. The tumor does not grow in bone or bone marrow.

About 80–90% of EMPs develop in the upper respiratory and digestive tracts. They can also develop in the bladder, lymph nodes, lungs, or other organs. However, the tumor can grow in soft tissue anywhere in the body.

Some people with EMP might develop a rare condition called multiple myeloma. This is when atypical plasma cells lead to the development of many tumors in the bone marrow.

Learn more about multiple myeloma, including its symptoms and treatment.

A 2021 study looked into the incidence rates of three types of plasma cell neoplasms — extramedullary plasmacytoma, multiple myeloma, and solitary plasmacytoma — in the United States from 2003 to 2016. It found that:

  • The overall incidence rate of extramedullary plasmacytoma was 0.09 adults in every 100,000.
  • The death rate for myeloma was 4.77 people in every 100,000. This figure included people with extramedullary plasmacytoma and multiple myeloma.
  • The highest incidence rates of extramedullary plasmacytoma, solitary plasmacytoma, and multiple myeloma were observable among non‐Hispanic black people compared with non-Hispanic white people. This difference may in part be due to genetic differences among both groups.
  • There could be a link between multiple myeloma and excess body weight.
  • People who were 80 years old or older had the highest rates of developing all three plasma neoplasms.

Scientists do not exactly know why some people develop extramedullary plasmacytoma. Some believe that certain factors, such as genetic disorders, viral infections, and exposure to high volumes of radiation, may contribute to the development of EMP.

Plasma cells develop from B lymphocytes, a type of white blood cell that the bone marrow produces. When invading bacteria or viruses enter the body of a healthy person, some of their B lymphocytes turn into plasma cells. The plasma cells make antibodies to fight the invaders and stop infection and disease.

In the case of plasma cell neoplasms, the process becomes unregulated and can lead to the development of benign or malignant tumors in the bones or soft tissues.

An extramedullary plasmacytoma can cause pain and other problems when it presses on nearby areas. However, the exact signs and symptoms will depend on where in the body the tumor forms.

For example, if it grows in the person’s throat, they may experience difficulty swallowing.

People with extramedullary plasmacytoma may receive a combination of therapies to manage their condition. These can include:

  • Surgery: This involves removing the tumor and may require additional treatment, which is known as adjuvant therapy, such as radiation therapy.
  • Radiation therapy: Healthcare professionals direct this therapy at the tumor and nearby lymph nodes. It involves treatment with high-energy X-rays or other types of radiation.
  • Chemotherapy: If the tumor grows or causes symptoms, a person may require drug treatment. Doctors can administer drugs by mouth or an injection into the veins or muscle, so that the medication can enter the bloodstream and reach the tumor.

People receive radiation therapy, chemotherapy, or both, to kill the atypical cells or stop them from dividing.

Like EMP, multiple myeloma is also a type of plasma cell neoplasm.

In about 15% of people with EMP, the disease can progress to multiple myeloma. A person with the condition may require lifelong monitoring to ensure that the disease does not progress.

In multiple myeloma, the tumors are in the bone marrow and spread throughout the body. In contrast, with EMP, the tumors are confined to a single site in the soft tissue. Additionally, EMP is a highly curable disease, while multiple myeloma is not.

According to the American Cancer Society, people with an EMP have excellent chances of survival if they do not develop more tumors.

Due to the low number of reported cases of EMP and variations in response to the disease, it is difficult to identify factors that can affect the prognosis of the condition. Some associated factors can include age, radiotherapy dose, size, and grade of the tumor.

EMP involves the development of a tumor in the soft tissue, and it usually develops in the nose, throat, or tonsils. While EMP is a type of plasma cell neoplasm, it rarely occurs in people.

The exact symptoms of the disease depend on where the tumor forms. It is typically treatable with surgery, radiation therapy, chemotherapy, or a combination of these treatments.