Multiple Myeloma: Immunomodulators, Proteasome Inhibitors and Anti-CD38
A drug once synonymous with human tragedy is now one of the pillars keeping myeloma patients alive for years longer than before. How did thalidomide come back — and what are the two warning labels you must never forget when you write for it? This is the story of the three modern backbones of myeloma therapy, and the plasma cell they were built to kill.
In the late 1950s a mild sedative was handed to pregnant women for morning sickness. Its name was thalidomide, and it caused thousands of babies to be born with phocomelia — limbs shortened to flippers. It became the definition of a medical catastrophe and was pulled from the world. Decades later, in a myeloma clinic, a physician writes a prescription for that very same drug — not as a sedative, but as a cancer therapy that will add years to a patient's life. The molecule never changed. What changed is that we finally understood it. And every prescription still carries, in bold, the warning its history burned into it.
The disease: a plasma cell gone rogue
Multiple myeloma is a malignancy of plasma cells. Plasma cells are the antibody factories of the immune system — mature B lymphocytes whose one job is to pump out immunoglobulin. In multiple myeloma (multiple myeloma) a single clone of plasma cells becomes malignant and floods the bone marrow, churning out one useless, identical antibody called a monoclonal protein or paraprotein (the M-protein). The marrow fills with tumour, healthy blood production is crowded out, and the bones themselves are eaten away.
The classic end-organ damage of myeloma spells CRAB: hyperCalcaemia (high calcium, from bone breakdown), Renal impairment (the paraprotein and calcium injure the kidneys), Anaemia (marrow crowded out), and Bone lesions — the punched-out lytic holes and pathological fractures that cause the deep bone pain patients describe. See CRAB in a patient with an M-protein, and myeloma is on the table.
Myeloma is incurable — but among cancers it is one of the great success stories of modern pharmacology. Median survival has stretched from a couple of years to well over a decade for many patients, driven almost entirely by the three drug backbones in this article, layered together. "Incurable" no longer means "untreatable."
Backbone 1 — Immunomodulatory drugs (IMiDs)
The IMiDs are thalidomide and its cleaner descendants lenalidomide and pomalidomide. Their mechanism was a mystery for years; we now know they bind a protein called cereblon, part of the cell's protein-disposal machinery. By hijacking cereblon they redirect which proteins get tagged for destruction — degrading transcription factors that myeloma cells depend on to survive. The net effect is threefold: a direct anti-myeloma action, an anti-angiogenic effect (starving the tumour of new blood vessels), and immune modulation (revving up T cells and natural killer cells against the cancer).
Thalidomide is the most infamous teratogen in the history of medicine — a single dose in early pregnancy can cause phocomelia. Because of this, thalidomide, lenalidomide and pomalidomide are dispensed only through strict pregnancy-prevention programmes: mandatory pregnancy testing, two forms of contraception, and controlled prescribing for anyone who could become or father a pregnancy. There is no such thing as a "one-off" IMiD prescription without this in place.
IMiDs markedly raise the risk of venous thromboembolism (VTE) — deep vein thrombosis and pulmonary embolism — especially when combined with dexamethasone. Every patient on an IMiD needs thromboprophylaxis: aspirin for lower-risk patients, or a prophylactic anticoagulant (low-molecular-weight heparin or a DOAC) for higher-risk ones. Thalidomide also causes a dose-dependent, sometimes irreversible peripheral neuropathy and marked sedation.
- IMiDs = thalidomide, lenalidomide, pomalidomide; they bind cereblon to redirect protein degradation.
- Actions: anti-myeloma, anti-angiogenic and immune-modulating.
- Teratogenic — dispensed only under strict pregnancy-prevention programmes.
- High VTE risk — every patient needs thromboprophylaxis (aspirin or anticoagulant).
- Thalidomide also causes peripheral neuropathy and sedation.
Backbone 2 — Proteasome inhibitors
Attack the factory's waste-disposal, and the factory chokes. A plasma cell is a protein factory running flat out, producing enormous amounts of immunoglobulin. Handling that workload generates a constant stream of misfolded, defective protein that must be shredded and recycled — a job done by the proteasome, the cell's molecular garbage disposal. Proteasome inhibitors — bortezomib, carfilzomib and the oral ixazomib — jam that machine. Defective protein piles up until the stress becomes lethal, and the plasma cell, more dependent on this clean-up than almost any other cell, is the first to die.
The signature toxicity of bortezomib is peripheral neuropathy — painful, tingling, glove-and-stocking sensory loss. A key practical fix: giving bortezomib subcutaneously instead of intravenously, and weekly rather than twice weekly, dramatically reduces the neuropathy while keeping the anti-myeloma effect. Carfilzomib spares the nerves but carries more cardiovascular risk instead.
Backbone 3 — Anti-CD38 monoclonal antibodies
The newest backbone is targeted antibody therapy. Malignant plasma cells display a surface marker called CD38 densely on their membrane. Monoclonal antibodies daratumumab and isatuximab lock onto CD38 and destroy the cell — flagging it for immune killing, triggering complement, and directly inducing cell death. Added to an IMiD-plus-steroid or bortezomib backbone, anti-CD38 antibodies deepen responses substantially and have reshaped both frontline and relapsed therapy.
CD38 is also present in small amounts on red blood cells. Anti-CD38 antibodies therefore interfere with blood crossmatching — they cause a false-positive antibody screen and can mask a genuine incompatibility. Always alert the transfusion lab that a patient is on daratumumab or isatuximab, and obtain a baseline blood group and antibody screen before starting the drug, so safe blood can still be provided.
- Proteasome inhibitors (bortezomib, carfilzomib, ixazomib) block protein disposal, killing the plasma cell.
- Bortezomib's main toxicity is peripheral neuropathy — reduced by subcut/weekly dosing.
- Anti-CD38 antibodies (daratumumab, isatuximab) target CD38 on plasma cells.
- Anti-CD38 antibodies interfere with transfusion crossmatch — warn the blood bank.
- The backbones are combined, not used alone — that is what drives the survival gains.
The partners: steroids, transplant and the bones
None of these backbones works alone. A corticosteroid — usually dexamethasone — is the near-universal partner, directly toxic to lymphoid cells and synergistic with every other agent (its immunosuppressive and metabolic effects link to the Inflammation and Endocrine sections). Eligible, fitter patients still go on to high-dose chemotherapy with an autologous stem-cell transplant, harvesting the patient's own marrow stem cells and returning them after intensive treatment. And the bone disease is managed in parallel: a bisphosphonate (zoledronic acid) or the RANKL antibody denosumab strengthens bone, cuts fractures, and treats the hypercalcaemia — the same bone-and-calcium pharmacology covered in the Endocrine (bone) section.
Notice the cross-links: monoclonal antibodies as a class (how they are named, how they work) are covered in the Lymphoma chapter; the corticosteroid partner in Inflammation and Endocrine; bisphosphonates and hypercalcaemia in Endocrine (bone); and VTE prophylaxis in Cardiovascular. Myeloma therapy is a crossroads where four other chapters meet.
- Starting an IMiD without a pregnancy-prevention programme — the single most dangerous omission with these drugs.
- Prescribing an IMiD (especially with dexamethasone) and forgetting VTE thromboprophylaxis.
- Missing bortezomib- or thalidomide-induced peripheral neuropathy until it becomes irreversible.
- Forgetting that anti-CD38 antibodies confound the transfusion crossmatch — not warning the blood bank.
Before starting daratumumab in a myeloma patient, which practical step is essential?
- Multiple myeloma = malignant plasma cells producing a paraprotein; damage spells CRAB (Calcium, Renal, Anaemia, Bone).
- IMiDs (thalidomide, lenalidomide, pomalidomide) bind cereblon — but demand pregnancy prevention AND VTE prophylaxis.
- Proteasome inhibitors (bortezomib) drown the plasma cell in its own misfolded protein; watch for neuropathy.
- Anti-CD38 antibodies (daratumumab, isatuximab) add depth but confound the transfusion crossmatch.
- Combined with dexamethasone, transplant and bone-directed therapy, these have made an incurable cancer very treatable.
- Katzung BG. Basic & Clinical Pharmacology — Cancer chemotherapy: immunomodulators, proteasome inhibitors & monoclonal antibodies.
- Hoffbrand AV, Moss PAH. Hoffbrand's Essential Haematology — Multiple myeloma & plasma cell disorders.
- Brunton LL, et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics — Targeted therapy of multiple myeloma.
- Rajkumar SV. Multiple myeloma: diagnosis, risk stratification and management (American Journal of Hematology review).
- National / NCCN & ESMO clinical guidelines — Multiple myeloma: IMiDs, proteasome inhibitors, anti-CD38 antibodies, VTE prophylaxis & pregnancy-prevention programmes.
