Multiple myeloma and leukemia are often confused because both are cancers that originate in the bone marrow. Both diseases fall under the broad category of hematological malignancies, involving the uncontrolled growth of abnormal blood cells. While they share this common starting point, the specific type of cell that becomes cancerous, the resulting symptoms, and the approach to treatment differ significantly.
Cellular Origin and Affected Blood Components
The fundamental difference between the two diseases lies in the specific blood cell line that becomes malignant. Multiple myeloma (MM) is a cancer of the plasma cell, a mature white blood cell that develops from B-lymphocytes. Plasma cells normally produce antibodies to fight infection. In MM, the cancerous plasma cells, called myeloma cells, accumulate primarily within the bone marrow, often forming tumor masses known as plasmacytomas.
This overgrowth of abnormal plasma cells crowds out healthy blood-forming cells, leading to low counts of red cells, white cells, and platelets. The malignant cells also produce excessive amounts of a non-functional antibody, known as monoclonal protein (M-protein), which circulates in the blood. Leukemia, by contrast, involves the uncontrolled proliferation of various types of white blood cells or their precursors in the bone marrow and blood.
Leukemia is classified based on whether it affects the lymphoid line (lymphocytes) or the myeloid line (red cells, platelets, and other white cells). Acute forms progress rapidly and are characterized by an overproduction of immature blood cells called blasts that flood the bone marrow and bloodstream. Chronic leukemias progress slowly and involve the excessive buildup of relatively mature but still abnormal white blood cells. Unlike the localized tumor growth seen in MM, leukemic cells are generalized, circulating widely in the peripheral blood.
Distinctive Clinical Manifestations
Because multiple myeloma and leukemia affect different cells and tissues, they generate distinct patterns of injury and symptoms. MM’s defining clinical features are summarized by the acronym CRAB: high Calcium, Renal problems, Anemia, and Bone lesions. Myeloma cells stimulate osteoclasts to break down bone tissue at an accelerated rate, causing bone pain, fractures, and lytic lesions visible on imaging.
The breakdown of bone releases calcium into the bloodstream, resulting in hypercalcemia, which can cause confusion, excessive thirst, and kidney damage. The large amounts of M-protein produced by the myeloma cells can also damage the kidneys, leading to renal insufficiency. Leukemia symptoms generally stem from the bone marrow’s inability to produce sufficient healthy blood cells due to the crowding effect of the malignant cells.
The lack of functional white blood cells causes frequent and severe infections, often presenting as persistent fevers. Low platelet counts (thrombocytopenia) lead to easy bruising, bleeding, and tiny red spots on the skin (petechiae). Anemia, resulting from a shortage of red blood cells, causes persistent fatigue, weakness, and shortness of breath in both diseases. While bone pain can occur in leukemia due to cell buildup, the destructive, lesion-forming bone damage seen in MM is not a hallmark of leukemia.
Treatment Strategies and Goals
The difference in cellular targets and disease behavior dictates divergent treatment strategies. Multiple myeloma treatment relies on targeted therapies and immunomodulatory drugs (IMiDs) to control the malignant plasma cells. Treatment typically involves combination therapy using agents like proteasome inhibitors and IMiDs, often with a corticosteroid.
The goal for most myeloma patients is not a complete cure but achieving and maintaining a deep, sustained remission, sometimes referred to as a functional cure. Many patients remain on continuous, low-dose maintenance therapy for years to prevent relapse, underscoring the chronic nature of the disease. High-dose chemotherapy followed by autologous stem cell transplantation (using the patient’s own stem cells) is an option for eligible patients to deepen the response.
Leukemia treatment depends on whether the disease is acute or chronic. Acute leukemia, which progresses rapidly, requires immediate, intensive induction chemotherapy to eradicate the cancer and achieve a cure. This intensive regimen often involves multiple phases, including induction and consolidation. The most aggressive forms often lead to allogeneic stem cell transplantation (using donor stem cells).
In contrast, certain slow-growing chronic leukemias, such as Chronic Lymphocytic Leukemia (CLL), may initially be managed with “watchful waiting.” Treatment is deferred until symptoms become troublesome or the disease progresses. When treatment is necessary, it is often less intense than for acute forms, utilizing targeted oral medications like tyrosine kinase inhibitors (TKIs) or novel targeted agents to manage the disease as a chronic condition.