Multiple myeloma doesn’t produce a visible tumor you can see or feel in most cases. It’s a blood cancer that grows inside bone marrow, so its “look” depends on where you’re looking: on imaging scans, it appears as distinctive holes in bone; in blood work, it shows up as abnormal proteins and low blood counts; and in the body, it presents as a pattern of symptoms affecting bones, kidneys, and energy levels. Rarely, it can form visible masses on or near the skin.
What It Looks Like on X-Rays and CT Scans
The most recognizable visual signature of multiple myeloma is what radiologists call “punched-out” lesions. These are round, sharply defined holes in bone that look as if someone used a hole punch on the skeleton. They show up as dark spots on X-rays because the bone in those areas has been destroyed by cancerous plasma cells. The skull is one of the most dramatic places to see them: a lateral skull X-ray of someone with advanced myeloma can show dozens of these circular holes scattered across the bone, each with clean edges and no surrounding reaction from the bone trying to heal itself.
This is different from many other cancers that spread to bone. Breast cancer or prostate cancer, for example, often trigger the bone to build new, abnormal tissue around the tumor. Myeloma almost exclusively destroys bone without rebuilding it, which is why the lesions look hollow and distinct. CT scans pick up these lytic lesions with even greater sensitivity, revealing damage that standard X-rays might miss, especially in the spine and pelvis.
What PET-CT Scans Reveal
PET-CT scans add a layer of information that regular imaging can’t provide: they show whether myeloma is actively growing. Active myeloma cells consume sugar at a high rate, so they light up brightly on a PET scan. The number of these “hot” lesions and their intensity correlate directly with how aggressive the disease is. Patients with highly active lesions on PET-CT at any point during treatment tend to have shorter remissions and worse overall outcomes.
PET-CT is also useful after treatment. Old bone damage from myeloma can persist on X-rays and CT scans long after the cancer is under control, making it hard to tell whether the disease is still active. A PET scan that no longer lights up suggests the remaining bone lesions are scars, not living cancer. This makes PET-CT one of the best tools for evaluating whether someone is truly in remission.
What It Looks Like in Blood Work
Myeloma produces a distinctive fingerprint on a blood test called serum protein electrophoresis. This test separates blood proteins by size and charge, and in a healthy person, the results form a smooth, gently sloping curve. In myeloma, a single sharp spike appears, called an M-spike or monoclonal spike. This spike represents the flood of identical, abnormal antibody proteins being pumped out by cancerous plasma cells.
The size of this spike helps distinguish myeloma from its precursor conditions. An M-spike below 3 g/dL, with less than 10% cancerous plasma cells in the bone marrow and no organ damage, points to a benign condition called MGUS, which may never cause problems. A spike at or above 3 g/dL, or bone marrow with 10% or more plasma cells but still no organ damage, indicates smoldering myeloma, a precancerous stage. Full-blown multiple myeloma is diagnosed when any level of M-protein is present alongside evidence of organ damage.
In urine, myeloma can show up as Bence Jones proteins, which are fragments of the abnormal antibodies small enough to pass through the kidneys. A 24-hour urine collection can detect these at concentrations as low as 10 mg/L. Their presence is a strong signal that myeloma should be investigated further.
The Four Signs of Organ Damage
Doctors use the acronym CRAB to describe what active myeloma looks like inside the body. Each letter stands for a type of organ damage that signals the disease has crossed from precancerous to requiring treatment.
- Calcium elevation. Myeloma breaks down bone, releasing calcium into the bloodstream. Levels above 11 mg/dL can cause excessive thirst, frequent urination, constipation, confusion, and nausea.
- Renal (kidney) problems. The abnormal proteins produced by myeloma can clog and damage the kidneys. A creatinine level above 2 mg/dL is the standard threshold for myeloma-related kidney dysfunction. Some patients progress to full kidney failure.
- Anemia. As myeloma crowds out normal blood-producing cells in the marrow, red blood cell counts drop. Hemoglobin below 10 g/dL is the clinical marker, and it translates to persistent fatigue, shortness of breath during routine activities, and pallor. Patients whose hemoglobin falls below 8.5 g/dL face significantly worse outcomes.
- Bone lesions. At least one area of bone destruction visible on imaging confirms this criterion. The spine, ribs, pelvis, and skull are the most common locations. These weakened bones fracture easily, sometimes from something as minor as lifting a bag of groceries.
What It Looks Like Physically
For most people, myeloma has no visible external signs. There’s no lump to find, no rash to notice. What patients typically experience first is bone pain, especially in the back or ribs, that doesn’t respond to usual painkillers and worsens over weeks. Unexplained fractures are sometimes the event that leads to diagnosis: a vertebra that collapses during normal activity, or a rib that breaks from a minor bump.
Fatigue from anemia is another early hallmark. It’s not the tiredness that improves with rest. It’s a deep, persistent exhaustion that makes even simple tasks feel draining. Some people notice they look paler than usual, or that they’re getting short of breath climbing stairs they used to handle easily.
In rare cases, myeloma can form visible masses outside the bone marrow, called extramedullary plasmacytomas. These soft tissue tumors most commonly appear in the head and neck region. They can emerge from facial bones as protruding lumps, develop on the scalp, or even appear near the eyelid. On the body, they may infiltrate muscles in the neck or back. These visible growths are uncommon and typically signal advanced or aggressive disease.
What Bone Marrow Looks Like Under a Microscope
The definitive “look” of myeloma comes from a bone marrow biopsy, usually taken from the hip bone. Under a microscope, normal bone marrow contains a diverse mix of developing blood cells at various stages. In myeloma, this diversity is replaced by sheets of plasma cells, which are larger than most marrow cells and have a distinctive appearance: an off-center, round nucleus with a pale area beside it, sometimes described as resembling a clock face or a fried egg.
In MGUS, these abnormal plasma cells make up less than 10% of the marrow. In active myeloma, they can range from 10% to over 90%, physically crowding out the cells responsible for producing red blood cells, white blood cells, and platelets. This overcrowding is what drives the anemia, increased infection risk, and easy bruising that many patients experience.
How Staging Reflects Severity
Once myeloma is confirmed, staging tells you how advanced it is. The Revised International Staging System uses two blood tests to sort patients into three stages. Stage I means relatively low tumor burden, with a specific blood protein (beta-2 microglobulin) at low levels and albumin still in a healthy range. Stage III reflects high tumor burden, often with genetic abnormalities in the cancer cells that make it more aggressive, including extra copies of chromosome 1 or deletions on other chromosomes.
Staging matters because it predicts how the disease will behave. Patients with stage I disease can have median survival measured in years to over a decade with modern treatments. Stage III patients face a more compressed timeline, though newer therapies continue to improve outcomes across all stages. The genetic profile of the myeloma cells, visible only through specialized lab testing on the biopsy sample, is increasingly important for guiding treatment decisions.