Smoldering Multiple Myeloma (SMM)

What Is Smoldering Multiple Myeloma?

Smoldering Multiple Myeloma (SMM), also called asymptomatic myeloma, is an intermediate condition between MGUS (benign) and active multiple myeloma (cancer).

Key characteristics of SMM:

Higher levels of abnormal protein than MGUS
More plasma cells in the bone marrow (10-60%)
No symptoms or organ damage
No treatment needed yet; active monitoring instead
May remain stable for years or progress to active myeloma

Important: SMM is not yet cancer requiring treatment. It is a pre-cancerous condition that requires careful monitoring.

How SMM Is Diagnosed

SMM is diagnosed when the following criteria are met:

M protein level: >= 3 g/dL in blood, or >= 500 mg/24 hours in urine
Bone marrow plasma cells: 10-60%
No symptoms or complications: No bone lesions, anemia, kidney dysfunction, or high calcium (no CRAB features)

If symptoms or organ damage develop, the diagnosis changes to active multiple myeloma.

SMM vs. MGUS vs. Multiple Myeloma

Feature	MGUS	SMM	Active Myeloma
M protein	< 3 g/dL	>= 3 g/dL	Variable (often high)
Plasma cells (bone marrow)	< 10%	10-60%	>= 10% (often higher)
Symptoms	None	None	Present (bone pain, fatigue, etc.)
Organ damage	None	None	Present (CRAB criteria)
Treatment	Monitoring only	Monitoring (or clinical trial)	Active treatment required
Progression risk	~1% per year	~10% per year (first 5 years)	N/A

Risk of Progression to Active Myeloma

SMM progresses to active multiple myeloma at a rate of approximately 10% per year for the first 5 years, then decreases over time.

Overall risk:

After 5 years: ~50% progress
After 10 years: ~65-75% progress
Some individuals remain stable for many years

Risk Stratification

Risk varies based on several factors:

Low-risk SMM:

Lower M protein levels
Lower plasma cell percentage
Normal free light chain ratio
Progression risk closer to MGUS (~5% per year)

High-risk SMM:

M protein > 2 g/dL
Bone marrow plasma cells > 20%
Abnormal free light chain ratio (<0.125 or >8)
Progression risk ~25% per year in the first 5 years

High-risk SMM may qualify for clinical trials evaluating early treatment.

Monitoring and Follow-Up

SMM requires more frequent monitoring than MGUS.

Typical monitoring schedule:

First year: Every 2-3 months
After 1 year (if stable): Every 3-4 months
After 2+ years (if stable): Every 4-6 months

Tests typically monitored:

M protein levels (blood and urine)
Complete blood count (CBC)
Kidney function
Calcium levels
Serum free light chains
Periodic imaging (X-ray, MRI, or PET/CT)

Symptoms That Require Immediate Attention

Contact your healthcare provider immediately if you develop:

Bone pain (especially back, ribs, or hips)
Fractures with minimal trauma
Severe fatigue or weakness
Frequent infections
Unexplained weight loss
Confusion or excessive thirst (possible high calcium)
Reduced urination or swelling (kidney issues)

These symptoms may indicate progression to active myeloma.

Treatment Considerations

Standard approach: Most individuals with SMM are monitored without treatment ("watchful waiting").

Why treatment is often delayed:

Not all SMM progresses
Treatments can have side effects
Early treatment has not consistently improved outcomes in low-risk SMM

When treatment may be considered:

High-risk SMM
Ultra-high-risk features suggesting imminent progression
Participation in clinical trials

Discuss potential options with your hematologist if you have high-risk features.

Living with SMM

Most people with SMM feel completely normal and can maintain their usual activities.

General recommendations:

Stay active to support bone health
Maintain a balanced diet with adequate calcium and vitamin D
Stay up to date with vaccinations (flu, pneumonia, COVID-19)
Stay well hydrated to support kidney function
Keep all monitoring appointments
Report new symptoms promptly

What About Clinical Trials?

If you have high-risk SMM, ask your doctor about clinical trials. Research is currently exploring:

Whether early treatment can delay progression
Which patients benefit most from intervention
New targeted therapies with fewer side effects

Clinical trials may provide access to emerging treatments.

Related Conditions

SMM exists on a spectrum:

MGUS: Earlier, lower-risk stage
Multiple myeloma: Active cancer requiring treatment
Waldenstrom macroglobulinemia: A different condition involving IgM proteins

The Bottom Line

SMM is a pre-cancerous condition that requires monitoring but usually not immediate treatment.

While the risk of progression is higher than MGUS, many people remain stable for years. The key is consistent monitoring to detect changes early.

Key takeaways:

You may feel completely normal; SMM typically has no symptoms
Not everyone progresses to active myeloma
Regular monitoring is essential
Treatment begins only if progression occurs
High-risk patients may benefit from clinical trials

Work with your healthcare provider to develop a personalized monitoring plan based on your risk profile.