Waldenström macroglobulinemia (WM) is a rare, slow-growing blood cancer in which abnormal white blood cells in the bone marrow overproduce a specific type of antibody called IgM. It affects roughly 3 to 4 people per million each year in the United States, making it one of the least common blood cancers. The disease causes problems in two ways: the cancerous cells crowd out healthy blood cells in the bone marrow, and the excess IgM protein thickens the blood and can damage organs throughout the body.
Where the Cancer Starts
WM originates from a type of immune cell that sits partway between a mature B cell and a plasma cell, sometimes called a lymphoplasmacytic cell. Normally, B cells mature into plasma cells that produce antibodies to fight infection. In WM, these in-between cells get stuck: they’ve undergone the genetic reshuffling that customizes an antibody but never completed the final switch that would change the antibody type from IgM to something else. The result is a clone of cells that multiplies in the bone marrow and pumps out large quantities of a single, identical IgM protein.
This matters because IgM is the largest antibody the body makes. When it accumulates in the bloodstream, it can make the blood abnormally thick, a condition called hyperviscosity. It can also act as an autoantibody, mistakenly attacking the body’s own nerves or red blood cells.
Common Symptoms
Many people with WM have no symptoms at the time of diagnosis. Their disease is discovered through routine blood work showing an elevated IgM level. When symptoms do appear, they tend to fall into two categories: those caused by the cancer cells crowding the bone marrow, and those caused by the excess IgM protein in the blood.
Bone marrow crowding leads to low blood counts. That can mean fatigue and shortness of breath from anemia, easy bruising or bleeding from low platelets, and frequent infections from reduced healthy white blood cells. Some people also develop an enlarged spleen or liver as the abnormal cells spread to those organs.
IgM-related symptoms are more distinctive. Roughly 20 to 30 percent of WM patients develop hyperviscosity syndrome, which can be the first sign of the disease. The classic presentation is a combination of neurological problems (headaches, dizziness, confusion, or even seizures), visual changes (blurred or double vision from swollen retinal veins), and mucosal bleeding (nosebleeds, bleeding gums, or gastrointestinal bleeding). Bleeding is the most common of these, driven by impaired platelet function in overly thick blood. Symptoms can begin when blood viscosity reaches about 3 centipoise but usually become noticeable above 4 to 5 centipoise, roughly three to five times the thickness of water.
In some patients, the IgM protein targets the body’s own tissues. It can bind to the protective coating around nerves, causing numbness, tingling, and weakness in the hands and feet. It can also clump together in cold temperatures, a phenomenon called cryoglobulinemia, which leads to poor circulation, skin color changes, and pain in the fingers and toes when exposed to cold.
Key Genetic Mutations
A mutation in a gene called MYD88 is found in the vast majority of WM cases, roughly 80 percent or more when tested with sensitive methods. This mutation sends a constant “survive and multiply” signal to the cancer cells, and its presence helps distinguish WM from other blood cancers that may look similar under the microscope.
A second mutation, in a gene called CXCR4, appears in about 35 to 43 percent of patients. CXCR4 mutations influence how well the disease responds to certain targeted treatments, making it an important factor when choosing therapy. Patients whose tumors carry this mutation sometimes show a slower or less complete response to some of the newer drugs.
How It Is Diagnosed
Diagnosis requires two things: detectable IgM protein in the blood and at least 10 percent infiltration of abnormal lymphoplasmacytic cells in a bone marrow biopsy. If the bone marrow shows less than 10 percent infiltration and IgM levels are below a certain threshold, the condition is classified instead as IgM monoclonal gammopathy of undetermined significance (IgM MGUS), a precursor state that progresses to symptomatic WM at a rate of about 1.5 percent per year.
Blood tests typically reveal the IgM spike on a protein electrophoresis test. The bone marrow biopsy confirms the diagnosis by showing the characteristic mix of small lymphocytes and plasma-like cells. Genetic testing for MYD88 and CXCR4 mutations is now standard practice and helps guide treatment decisions.
Treatment Options
Not everyone diagnosed with WM needs treatment right away. If you have no symptoms and your blood counts are stable, your doctor may recommend a watch-and-wait approach with regular monitoring. Treatment is typically started when symptoms develop, blood counts drop significantly, or organ damage appears.
The most significant advance in WM treatment has been a class of drugs called BTK inhibitors, which block a key survival signal inside the cancer cells. Ibrutinib was the first to gain FDA approval for WM, and in clinical trials it produced a response in about 90 percent of previously treated patients, with nearly 80 percent achieving a major response at roughly five years of follow-up. Zanubrutinib, a newer BTK inhibitor, showed comparable effectiveness in a head-to-head trial: 94 percent overall response versus 93 percent for ibrutinib, with similar progression-free survival at 18 months. Zanubrutinib tends to cause fewer cardiovascular side effects like irregular heartbeat and high blood pressure, which has made it a preferred option for many patients.
Other treatment approaches include chemotherapy-based regimens, sometimes combined with the antibody rituximab, which targets a marker on the surface of the cancer cells. One important note: rituximab can temporarily spike IgM levels in WM patients. For those who already have thick blood (IgM above 4 g/dL), doctors often use plasmapheresis first to bring IgM levels down before starting rituximab.
Plasmapheresis, a procedure that filters excess IgM out of the blood, is also the go-to emergency treatment for hyperviscosity syndrome. It provides rapid symptom relief, often within hours, and serves as a bridge to longer-term therapy.
Prognosis and Survival
The overall five-year relative survival rate for WM is about 78 percent, based on data from the National Cancer Institute. But that number spans a wide range depending on individual risk factors. Doctors use a scoring system based on five characteristics: age over 65, low hemoglobin, low platelet count, elevated beta-2 microglobulin (a protein that reflects tumor burden), and high IgM levels. Patients in the lowest risk group have a five-year survival rate around 95 percent, while those in the highest risk category are closer to 36 percent.
WM is generally considered a treatable but not curable disease. Many patients live with it for years or even decades, going through periods of treatment and remission. The introduction of BTK inhibitors and other targeted therapies has steadily improved outcomes, and patients diagnosed today have more effective, better-tolerated treatment options than those available even a decade ago.