Multiple myeloma often spreads to affect more than one part of the body. “In my case, myeloma spread through all the main bones,” one MyMyelomaTeam member said. “I had to have spinal surgery to prevent six vertebrae from collapsing.”

Myeloma might appear to metastasize (spread) like breast or lung cancer, but it behaves differently. As a systemic cancer of the blood and bone marrow, it can develop in marrow throughout the body from the outset. This is different from spreading outward from a single primary tumor.

Read on to explore how multiple myeloma spreads, its most common locations, and how doctors describe its progression.

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Does Multiple Myeloma Metastasize?

Unlike solid tumors such as breast or lung cancer, myeloma rarely follows a traditional spreading pattern. It’s typically a systemic cancer. This means it affects bone marrow throughout the body rather than spreading outward from one tumor.

Rarely, myeloma cells can spread outside the bone marrow to soft tissues, organs, or even the brain and spinal cord.

How Multiple Myeloma Is Diagnosed

A plasma cell tumor found in one area of the body is called a solitary plasmacytoma. If plasma cells cause a tumor in the bone, it’s called a solitary plasmacytoma of bone (SPB). SPB is often found in the ribs, femur, spine, and pelvic bone.

Diagnosing multiple myeloma involves different steps than identifying a solitary plasmacytoma. To make a diagnosis, doctors typically look for a biopsy-confirmed plasma cell tumor or at least 10 percent abnormal plasma cells in the bone marrow.

Doctors also check for signs of related organ damage using the acronym CRAB. This stands for elevated calcium levels, renal (kidney) damage, anemia, and bone lesions.

In some cases, specific lab markers known as myeloma-defining biomarkers can signal active disease. This may confirm the diagnosis even before these physical complications appear.

Without CRAB features or myeloma-defining biomarkers, someone with abnormal plasma cells may be diagnosed with smoldering myeloma instead. This is an earlier form of the disease that isn’t causing symptoms yet. It doesn’t always need immediate treatment.

How Multiple Myeloma Moves Through the Body

Although multiple myeloma generally develops at different sites at the same time, myeloma cells can leave the bone marrow through the bloodstream, just as normal immune cells leave the bone marrow to help fight infection. From there, they can settle in new areas and form more tumors.

Common Bones Affected by Multiple Myeloma

Myeloma often affects several bones at once. This includes the spine and ribs, where it can cause bone damage leading to fractures and abnormally high calcium levels. The bones most commonly affected include:

• Pelvis
• Spine
• Long bones (like the femur)
• Skull
• Ribs

Myeloma cells slowly destroy the bone. That’s why people with multiple myeloma typically complain of having bone pain, often in their back. This symptom can be easily overlooked, since back pain can be caused by many factors.

People with back pain that doesn’t improve, or that’s severe, unusual, or paired with other symptoms, should see their doctor. But myeloma isn’t limited to the bones — it can also spread beyond them.

Extramedullary Disease: When Myeloma Spreads Beyond the Bone

Sometimes, myeloma cells break through the bone and grow into surrounding soft tissue. Doctors refer to this as paraskeletal extension, or bone-related spread. It’s the most common way the cancer reaches beyond the bone marrow.

True extramedullary disease (EMD) is different. It occurs when myeloma cells travel through the bloodstream and form tumors in soft tissues or internal organs with no connection to bone. Doctors consider this a more aggressive type of myeloma.

Extramedullary myeloma can develop in:

• Skin or nearby soft tissue (most common at diagnosis)
• Lymph nodes
• Liver, kidneys, or spleen
• Breast or pleural tissue
• Sinuses, nasal cavities, larynx, or upper throat

True EMD is relatively uncommon. Research suggests it affects about 0.5 percent to 4.8 percent of people when they’re first diagnosed with myeloma. It also affects 3.4 percent to 14 percent among those experiencing a relapse — when cancer returns after a period of improvement.

The numbers vary across studies. This is largely because researchers haven’t always defined extramedullary disease in the same way.

Can Multiple Myeloma Spread to the Brain?

In very rare cases, multiple myeloma can reach the brain, the spinal cord, or the protective fluid around them. Doctors call this central nervous system (CNS) involvement. It’s an uncommon type of extramedullary disease.

CNS involvement affects less than 1 percent of people with multiple myeloma. It typically develops at relapse, though it can occasionally appear when myeloma is first found.

CNS involvement can cause a wide range of symptoms. This includes confusion, vision changes, or weakness.

Because these can overlap with symptoms from myeloma itself or its treatment, CNS involvement isn’t always easy to recognize right away. Let your care team know promptly about any new or worsening neurological symptoms.

Research indicates that CNS involvement can be more challenging to treat than other forms of relapse. But newer treatment approaches are constantly evolving, and your doctors can help you understand the best options for your specific care plan.

How Often Does a Solitary Plasmacytoma Progress to Multiple Myeloma?

A solitary plasmacytoma is a single plasma cell tumor, either in bone (SPB) or in soft tissue (EMP). This is uncommon on its own. SPB occurs in about 0.45 out of every 100,000 people in the U.S. each year, according to data from 2003 to 2016.

How often it progresses to full multiple myeloma varies by study. A 2026 multicenter study found that about 76 percent of people with SPB eventually progressed to multiple myeloma. This is compared with about 92 percent of those who had minimal bone marrow involvement at diagnosis.

An earlier study from the Netherlands based on data from 1988 to 2011 found a similar pattern. Seventy percent of people with SPB progressed to multiple myeloma, along with 12 percent of people with EMP.

Why Multiple Myeloma May Not Be Caught Early

Multiple myeloma can be hard to detect early. This is mainly because many of its symptoms overlap with more common conditions. Back pain, nausea, loss of appetite, fatigue, constipation, and excessive thirst can all point to myeloma — or to something else entirely.

Some people don’t have any symptoms at all. Instead, they find out they have myeloma after a routine blood test done for another reason flags something unusual. These are often the same warning signs used in diagnosis, like high calcium, anemia, or kidney changes.

These signs can be easy to miss or mistake for something else. That’s why multiple myeloma diagnoses are often made later, once the condition has become more advanced. Although there is no screening strategy recommended yet, regular checkups and blood work can help catch changes sooner.

Navigating What Comes Next

Myeloma usually affects multiple areas of the bone marrow rather than spreading, or metastasizing, like a solid tumor. In some cases, myeloma cells can extend beyond the bone marrow into nearby soft tissue or other organs.

Although there’s currently no cure, treatments continue to improve. Understanding how myeloma behaves can help you and your care team respond to changes.

If you’re living with multiple myeloma, keep a simple log of new or worsening symptoms. This may include back pain, weakness, numbness, or other neurological changes. Having specific details ready for appointments can help your care team decide whether further evaluation is needed.

You can also ask your hematologist-oncologist — a doctor who specializes in blood cancers — how widely your myeloma involves the bone marrow. They can also tell you whether there’s disease outside the bone marrow and what your test results mean for your diagnosis and outlook.