Is multiple myeloma a form of cancer and does a tumor in the iliac bone indicate stage 4 cancer?

Is Multiple Myeloma Cancer and Does Iliac Bone Involvement Mean Stage 4?

Yes, multiple myeloma is definitively a cancer—specifically a malignancy of plasma cells in the bone marrow—and no, a tumor in the iliac bone does NOT automatically mean stage 4 disease. 1, 2, 3

Multiple Myeloma as Cancer

• Multiple myeloma is a plasma cell neoplasm that accounts for 1-1.8% of all cancers and represents the second most common hematological malignancy. 1
• It results from neoplastic proliferation of plasma cell clones that accumulate in the bone marrow and produce monoclonal immunoglobulin (M-protein). 2, 3
• The disease is characterized by clonal bone marrow plasma cells ≥10% or biopsy-proven plasmacytoma, plus evidence of end-organ damage or specific myeloma-defining biomarkers. 2, 4

Staging Systems: Why Bone Involvement ≠ Stage 4

Critical clarification: Multiple myeloma does NOT use the traditional TNM staging system that other solid tumors use. The presence of bone lesions (including in the iliac bone) is actually part of the diagnostic criteria for myeloma itself, not a marker of advanced stage. 1, 2

The Durie-Salmon Staging System (Older System)

• This older system classifies myeloma into stages I, II, and III based on hemoglobin, calcium, M-protein levels, urine light chains, and bone lesions. 1
• Even in this system, bone lesions are present across all stages—"normal bone structure" in Stage I, "minor bone lesions" in Stage II, and "advanced bone lesions" in Stage III. 1
• There is no "Stage 4" in the Durie-Salmon system. 1

The International Staging System (ISS) - Current Standard

• The ISS categorizes myeloma into three stages (I, II, III) based on serum β-2 microglobulin and serum albumin levels—NOT on the location or presence of bone lesions. 4
• The Revised ISS incorporates high-risk cytogenetics [t(4;14), t(14;16), t(14;20), del(17p)] in addition to ISS parameters. 4
• Again, there is no "Stage 4" in this system. 4

What Bone Involvement Actually Means

• Bone lesions (including lytic lesions in the iliac bone) are part of the CRAB criteria (hypercalcemia, Renal insufficiency, Anemia, Bone lesions) used to diagnose symptomatic multiple myeloma requiring treatment. 2, 4, 5
• Approximately 79% of patients have osteolytic bone disease at presentation, making bone involvement extremely common and not indicative of "metastatic" or "stage 4" disease. 6
• The iliac bone is a common site for myeloma involvement because myeloma originates in the bone marrow itself—it's not spreading from elsewhere. 3, 5

Key Takeaway

Multiple myeloma is fundamentally different from solid tumors. It is a bone marrow-based cancer where bone involvement is expected and part of the disease definition, not evidence of distant metastasis. The staging systems (Durie-Salmon and ISS) do not include a "Stage 4," and prognosis depends on laboratory markers (β-2 microglobulin, albumin, LDH) and cytogenetic features rather than anatomic extent of bone disease. 1, 4, 6