Plasmacytoma is a rare condition characterized by the abnormal growth of malignant plasma cells, a type of white blood cell. Normally, plasma cells produce antibodies (immunoglobulins) that protect the body from infection. In plasmacytoma, these cells multiply uncontrollably, forming a single, localized tumor mass.
Defining the Condition and Its Forms
Plasmacytoma is a localized collection of malignant plasma cells without evidence of systemic disease. These abnormal cells often produce a non-functional antibody, known as a monoclonal protein (M-protein), detectable in the blood or urine. Classification is based on the tumor’s location, dividing the condition into two types.
Solitary Bone Plasmacytoma (SBP) occurs exclusively within a single bone and accounts for the majority of cases. SBP typically arises in the axial skeleton, most commonly affecting the vertebrae of the spine or the pelvis. This form originates from plasma cells within the bone marrow.
Extramedullary Plasmacytoma (EMP) forms in soft tissues outside the bone marrow and skeletal system. EMP most frequently appears in the head and neck region, particularly the upper respiratory tract, including the nasal cavity, sinuses, and throat. Both SBP and EMP are defined by their solitary nature and the absence of widespread plasma cell involvement.
Recognizing the Signs
Symptoms vary significantly depending on the tumor’s location. For Solitary Bone Plasmacytoma (SBP), the most common symptom is localized pain. The growth of malignant cells can erode the bone, potentially leading to pathological fractures, where the bone breaks without significant injury.
If SBP is located in the spine, the expanding tumor can press on the spinal cord or nerve roots, causing nerve compression. This compression may result in sharp, radiating pain, weakness, or loss of function in the limbs or bladder. Less common skull tumors can cause headaches, dizziness, or vision problems.
Extramedullary Plasmacytoma (EMP) often presents as a palpable mass in the soft tissue. When EMP occurs in the upper respiratory tract, symptoms relate to obstruction or local pressure. These include difficulty breathing through the nose, chronic nasal discharge, or nosebleeds. Tumors in the throat can cause difficulty swallowing or a persistent sore throat.
Establishing a Diagnosis
Diagnosis confirms the presence of a localized plasma cell tumor while ruling out Multiple Myeloma (MM), a systemic disease. The most definitive diagnostic tool is a biopsy, which involves taking a tissue sample from the suspected tumor for microscopic examination. This analysis confirms the presence of malignant plasma cells.
Imaging studies locate the tumor and determine its extent. X-rays and computed tomography (CT) scans visualize bone damage, particularly lytic lesions characteristic of SBP. Magnetic resonance imaging (MRI) and Positron Emission Tomography (PET) scans provide detailed images of bone and soft tissue, helping confirm the solitary nature of the lesion and screen for other potential disease sites.
Blood and urine tests look for M-protein, the abnormal antibody produced by malignant plasma cells. M-protein levels are generally lower in plasmacytoma than in Multiple Myeloma. Testing also includes a complete metabolic panel to assess organ function, checking for systemic involvement like elevated calcium or impaired kidney function. A bone marrow biopsy is mandatory to ensure the disease is truly localized. Plasmacytoma diagnosis requires the bone marrow to contain less than 10% abnormal plasma cells, confirming the absence of widespread infiltration.
Therapeutic Approaches
Treatment for localized plasmacytoma is typically approached with curative intent. Radiation therapy is the primary modality for both Solitary Bone Plasmacytoma (SBP) and Extramedullary Plasmacytoma (EMP). Plasma cell tumors are highly sensitive to radiation, and localized radiotherapy aims to destroy tumor cells while sparing surrounding healthy tissue.
The standard radiation dose for effective local control is typically 40 to 50 Gray (Gy), administered over several weeks. This localized treatment achieves a high rate of local control, often above 80%, for both bone and soft tissue tumors, resulting in a lasting cure for many patients.
Surgery is reserved for specific situations, not as a routine primary treatment. For SBP, intervention may be required to stabilize a bone at high risk of fracture or to relieve nerve compression, particularly in the spine. For EMP, surgery may remove the tumor if it is easily accessible and necessary to restore function, such as clearing an obstructed airway.
Systemic therapies, such as chemotherapy or novel agents, are generally not used as first-line treatment for localized plasmacytoma. These treatments are reserved for cases where the tumor is very large, the disease shows signs of progression, or if high-risk features exist. Combining radiation with systemic agents may improve the time before the disease progresses to Multiple Myeloma.
The Connection to Multiple Myeloma
Plasmacytoma is a localized form of plasma cell cancer existing on a spectrum with Multiple Myeloma (MM), a systemic plasma cell malignancy. The primary concern after successful local treatment is the risk of progression to widespread MM over time. This occurs because the malignant plasma cell clone, though initially localized, may eventually spread throughout the bone marrow.
The risk of progression is significantly higher for SBP than for EMP. Up to 65% to 84% of SBP patients may progress to MM within 10 years, requiring long-term vigilance. Extramedullary plasmacytoma carries a lower risk, with 25% to 35% of EMP cases developing into MM over the same period.
Given this substantial risk, patients require regular and lifelong follow-up monitoring after treatment. Surveillance typically involves periodic blood and urine tests to monitor M-protein levels. It also includes an annual imaging scan to detect any new bone or soft tissue lesions. The goal is to identify signs of transformation to MM at the earliest possible stage.