Cutaneous plasmacytoma is a rare condition that affects the skin. Diagnosing it may be difficult and doctors might use a variety of tests. Treatment can depend on the severity and cause of the condition, among other factors.

Cutaneous plasmacytoma may be a primary form of cancer, which means that it affects the skin first. It can also occur as a complication of multiple myeloma or plasmacytoma in the blood, in which case doctors classify it as secondary.

Without treatment, plasmacytoma can progress to multiple myeloma, which is cancer of blood plasma cells. This progression usually takes 2–3 years. Multiple myeloma is more difficult to treat, with a higher death rate than plasmacytoma.

Read on to learn more about plasmacytoma, including how doctors diagnose and treat the condition.

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Plasmacytoma is a tumor that begins in the plasma cells of a person’s bones or soft tissue. Plasmacytoma can also occur in the intermediate phase between two other conditions, monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma.

In people with MGUS, an abnormal monoclonal protein, M protein, is present in the blood and is a major risk factor for plasmacytoma.

Types of plasmacytoma include the following:

  • Solitary plasmacytoma of bone (SPB): This is the most common type. It sometimes spreads into the bone marrow. This type of plasmacytoma is more likely to progress to multiple myeloma and be fatal.
  • Extramedullary plasmacytoma (EMP): This cancer forms in soft tissue cells and can occur at any site. EMP is less common than SPB. Around 2–4% of extramedullary plasmacytomas have skin or cutaneous involvement.
  • Cutaneous plasmacytoma: This is a rare manifestation of plasmacytoma that occurs when cancer affects the skin.

Primary versus secondary

Doctors may also refer to primary cutaneous plasmacytoma as primary extramedullary plasmacytoma. This can occur when cancer appears first in the skin.

Primary cutaneous plasmacytoma is a very uncommon presentation of the disease. Therefore, if a person has plasmacytoma of their skin, a doctor may suspect plasmacytoma or myeloma elsewhere in the body.

Secondary cutaneous plasmacytoma happens when either plasmacytoma or multiple myeloma spread from the original site to the skin.

Learn more about extramedullary plasmacytomas.

Plasmacytoma is a rare cancer. Plasma cell cancers comprise about 1% of all cancers.

Plasmacytoma is rarer still. SBP makes up 2–5% of plasma cell cancers, with EMP contributing an additional 4% of cases. Secondary cutaneous plasmacytoma may happen when these cancers spread.

Primary cutaneous plasmacytoma is rare enough that no specific data exist on its prevalence. According to a 2019 case report, the scientific literature contains published accounts of only 68 prior cases.

Anyone can get plasmacytoma. However, it is more common among the following individuals:

  • People of advanced age: Most people with plasmacytoma are aged 55–60.
  • Males: Males are roughly twice as likely as females to develop plasmacytoma.
  • African Americans: People of Color experience many diseases at higher rates than others because of systemic and healthcare racism that affects other risk factors.
  • Those exposed to toxic material: Some research suggests that exposure to toxic chemicals or ionizing radiation may increase the risk of plasmacytoma.
  • Those exposed to certain viruses: Research suggests that viruses may cause certain cancers. The Epstein-Barr virus may be a risk factor for blood cell cancers, including plasmacytoma.

It is possible to have plasmacytoma and no symptoms or to have symptoms that are mild or recurring.

People with primary cutaneous plasmacytoma can develop lesions on the skin. One 2021 case study suggests that a person with primary cutaneous plasmacytoma can present with multiple nodules. These nodules appear tender, firm, and red to violet in color. The skin lesion in the 78-year-old man featured in the study showed signs of crusting and erosion.

Secondary cutaneous plasmacytoma may develop from plasmacytoma in the bones or multiple myeloma. As a result, people often develop unexplained bone pain or tenderness around the bones, especially on the breast bone or pelvis. Other symptoms may include:

Plasmacytoma may also cause weight loss, but this is not typical during the early stages.

It can be challenging for doctors to diagnose plasmacytoma since it mimics several other conditions. The process usually begins with a complete medical history and a medical exam to look for injuries or infections that might explain symptoms.

A doctor will typically order tests, including:

  • Bloodwork: A doctor may look for M proteins in the blood serum.
  • Urine tests: There may also be M proteins in the urine.
  • Imaging studies: A doctor may order imaging tests such as MRI or CT scans. These tests may look at a single lesion to see how it has developed or scan the entire body for other lesions.
  • Biopsy: A biopsy involves removing a small culture of the area a doctor thinks contains cancer, usually using a needle. The doctor will then assess the sample. A pathologist may look for tumors or plasma cell accumulations in these samples.

Learn more about how doctors diagnose multiple myeloma.

Treatment for plasmacytoma depends on the person’s health and the condition’s progression. Some options include:

  • Radiation therapy: This is the treatment of choice and has an 80% control rate for SPB and EMP.
  • Chemotherapy: Doctors may use this as an additional form of therapy, or adjuvant therapy, alongside other methods.
  • Surgery: A doctor may remove a portion or the whole of the tumor to diagnose the cancer type or treat the cancer.
  • Autologous stem cell transplant: People with multiple or high risk lesions may benefit from stem cell transplants.

A person’s outlook depends on the type of cancer they have. People with multiple myeloma that have cutaneous involvement may have a less positive outlook.

An important factor for predicting the outcome of primary cutaneous plasmacytoma may be the number of skin lesions a person presents with.

People should note that primary cutaneous plasmacytoma is rare. As a result, it is difficult to quote specific survival data.

Plasmacytoma survival rates

Data on other forms of plasmacytoma may help guide a person in assessing their outlook.

SBP has a less positive outlook than EMP. SBP progresses to multiple myeloma in 50% of cases, usually within 3 years. EMP progresses to myeloma in about 15% of cases.

Factors that can worsen the prognosis of a person with SBP include:

  • being over the age of 40
  • having lesions larger than 5 centimeters in size or spinal lesions
  • having low bone density or osteopenia
  • having neurological symptoms
  • having high levels of M proteins

According to the American Cancer Society, the 5-year survival rate for localized plasmacytoma is 78%. This means people with plasmacytoma are 78% as likely as those without the condition to be alive 5 years after their diagnosis. When plasmacytoma progresses to multiple myeloma, the overall 5-year survival rate falls to 55%.

Plasmacytoma is similar to several other blood cancers. When comparing symptoms, a doctor may also consider the following diagnoses:

  • Multiple myeloma: Plasmacytoma is a localized cancerous tumor, while multiple myeloma causes multiple plasma cell tumors. People with multiple myeloma also tend to have systemic disease. Doctors sometimes use the acronym CRABS to look for common multiple myeloma symptoms — hypercalcemia, renal failure, anemia, and bone disease.
  • Plasmablastic lymphoma: This type of lymphoma is more common in people with weakened immune systems due to conditions such as HIV and AIDS. Under a microscope, tumors from this type of lymphoma have plasmablast cells.
  • Reactive plasmacytosis: Plasmacytosis means there is a high number of plasma cells in the tissue or blood. Plasmacytoma cells show light chain restriction under a microscope, while reactive plasmacytosis does not.
  • Non-Hodgkin lymphoma: This condition can look similar to plasmacytoma. Doctors distinguish between the two by checking for the expression of CD19 and CD45 genes in cells. These are present in lymphoma but absent in plasmacytoma.

Plasmacytoma is a type of local cancer that has not spread or metastasized to other areas of the body. It affects bone and soft tissue. It may also affect the skin.

In the early stages, cutaneous plasmacytoma is very treatable. However, it has a high risk of evolving into multiple myeloma, which is often aggressive. A person who develops cutaneous plasmacytoma as a complication of myeloma may have a less positive outlook.

People with bone pain, weakness, fatigue, or any other cancer symptoms should promptly contact a doctor. Early diagnosis and treatment can be lifesaving, prevent or slow cancer progression, and reduce the risk of serious complications.