Plasmacytoma and multiple myeloma (MM) are two types of cancer that affect plasma cells. There are several differences between these two types of cancer. Many people with plasmacytoma go on to develop MM.

Plasma cells are a type of white blood cell. They normally function by making antibodies to help defend you against germs such as viruses and bacteria.

Sometimes, cancer can affect plasma cells. Two examples of this are plasmacytoma and multiple myeloma (MM). While these conditions are both plasma cell cancers, there are also key differences to be aware of.

Plasma cell cancers happen when plasma cells begin growing and dividing out of control. When this happens, they can form tumors.

A plasmacytoma is a plasma cell tumor that can form in the bone or in the soft tissues of your body. Read more about plasmacytoma.

Multiple myeloma (MM) is when a dysfunctional form of plasma cells develops in your bone marrow and reproduces quickly, crowding out the production of other important blood cells produced by your bone marrow.

In addition to growing uncontrollably, the dysfunctional plasma cells, and to a lesser extent, plasmacytoma, produce an abnormal antibody called M protein. High concentrations of M protein can cause health complications.

Read more about MM.

While plasmacytoma and MM do have similarities, they also have key differences in things such as:

  • tumors
  • symptoms
  • diagnosis
  • staging
  • treatment

We review in more detail each of these key differences below.

Tumors: Number and location

Generally speaking, the cancer cells in a plasmacytoma typically form a tumor at a single location. This is called a solitary plasmacytoma.

There are two types of plasmacytomas:

  • Solitary plasmacytoma of the bone (SPB): SPB occurs in a bone, most commonly those of your spine, ribs, or skull. The incidence of SPB is 40% higher than that of extramedullary plasmacytoma.
  • Extramedullary plasmacytoma (EMP): EMP happens in soft tissue. It’s most often found in the head and neck area, such as your throat, sinuses, and tonsils.

In contrast, abnormal growths of plasma cells in MM can be found in the bone marrow of many bones in your body. Unlike plasmacytomas, they’re not found in soft tissues.


SPB can lead to bone pain and weakness, which increases the risk of bone breaks. When the bones of the spine are involved, SPB can also cause spinal cord compression.

Meanwhile, an EMP can press on nearby tissues. This can cause pain and other problems. For example, an EMP in your sinuses can lead to symptoms such as headache, runny nose, and nasal obstruction.

In MM, cancer cells build up in your bone marrow. This crowds out healthy blood cells, leading to low blood counts that can cause:

  • anemia
  • an increased risk of infections
  • easy bleeding

The effects of MM also cause characteristic organ damage throughout the body. These are referred to as “CRAB symptoms” and include:


While many of the diagnostic tests for plasmacytoma and MM are similar, each condition has different diagnostic criteria. This is a set of symptoms, signs, or test results used to accurately diagnose a condition.

Plasmacytoma can be diagnosed when all of the following are true:

  • A lesion of abnormal plasma cells is found in the bone or in soft tissue.
  • The abnormal plasma cells are clonal, meaning that they’re derived from a common ancestor cell.
  • Bone marrow is normal or contains less than 10% cancer cells.
  • A skeletal survey is normal, aside from the original lesion.
  • There’s no evidence of CRAB symptoms.

Meanwhile, MM is diagnosed when both of the following are true:

  1. A clonal, or duplicate, population of abnormal plasma cells of 10% or more in the bone marrow or a biopsy-confirmed plasmacytoma is present.
  2. Any one or more of the following things are true:
    • There’s evidence of CRAB symptoms.
    • More than one bone lesion is found using imaging.
    • There’s a population of clonal plasma cells in your bone marrow at 60% or more, with or without CRAB symptoms.
    • Your serum free light chain ratio is elevated, and the concentration of free light chain is 100 milligrams per liter (mg/L) or higher.


Staging is a reflection of the extent of the cancer in your body. There’s no standard staging system for plasmacytoma.

Meanwhile, MM is typically staged using the RISS system. This system gives an idea of the extent of your cancer as well as your outlook. It’s based on:

  • Beta-2-microglobulin (B2M): B2M is found on the surface of plasma cells and is at higher levels in MM.
  • Albumin: Albumin is an important protein found in blood plasma. It’s found at lower levels in MM.
  • Lactate dehydrogenase (LDH): Elevated LDH levels can signal tissue damage and more advanced MM.
  • Genetics: Certain genetic changes in MM are associated with a poorer outlook for people with cancer.
StageB2M levels
Stage 1B2M levels are less than 3.5 mg/L, albumin levels are 3.5 grams per deciliter (g/dL) or higher, LDH levels are normal, and genetics aren’t high risk.
Stage 2This isn’t stage 1 or 3.
Stage 3B2M levels are 5.5 mg/L or higher, LDH levels are high, or cytogenetics are high risk.


Plasmacytomas can often be treated with radiation therapy and sometimes chemotherapy. Additionally, it’s sometimes possible to remove EMPs using surgery.

People with smoldering MM often don’t require treatment immediately. Instead, they’re monitored carefully, and treatment begins when symptoms develop. Some people with smoldering MM never develop active MM.

Active MM can be treated using one or a combination of therapies. These may include:

Radiation therapy can also be used to ease bone pain from MM. This is called palliative care. Additionally, radiation therapy and surgery can also be used to prevent serious complications from spinal cord compression in MM.

Now let’s explore the different aspects of progression for plasmacytomas and MM.


The outlook for people with plasmacytoma is typically very good when treatment is given. For example, radiation therapy for plasmacytoma can result in a control rate of 80%.

But plasmacytoma can progress into MM. This is more common in SPB than in EMP. A 2019 study of 66 people found that progression to MM happened within 5 years for 47.2% and 8.3% of people with SPB and EMP, respectively.

Some factors that are associated with a poorer outlook for people with plasmacytoma include:

  • older age
  • larger tumor size
  • SPB that affects your spine
  • clonal abnormal plasma cells found in your bone marrow
  • M protein that persists after treatment

As such, individuals treated for plasmacytoma will need regular follow-ups to check on the recurrence or the development of MM.

Multiple myeloma

If you have smoldering MM, your risk of progression to active MM is about 10% per year in the first 5 years after receiving a diagnosis. The risk of progression typically decreases after 5 years.

People with MM can also develop both SPB and EMP. It’s estimated that 3.5% to 18% of people who newly received a diagnosis MM also have plasmacytoma.

The National Cancer Institute (NCI) notes that people who have plasmacytoma, specifically soft tissue, in conjunction with MM typically have a poorer outlook.

According to the NCI, MM is very treatable but typically isn’t curable. The 5-year survival rate for MM is 59.8%. Factors that can influence your outlook include:

  • the stage of your MM
  • the genetics of your MM
  • the type of treatment used and how your MM responds to it
  • your level of kidney function
  • your age and overall health

Plasmacytoma and MM are both cancers that affect plasma cells. But these cancers have many differences in things such as basic characteristics, symptoms, diagnosis, and treatment.

Generally, the outlook for people with plasmacytoma is good. Many people eventually do go on to develop MM sometime in the future. While MM is very treatable, it typically can’t be cured.