5 Hematopoietic Growth Factors
- Myeloid GFs for 1° prophylaxis: FN risk >20% w/ chemo
- G-CSF 1st-line; pegfilgrastim (peg-CSF) single dose, ↓ FN ~50% vs std G-CSF
- 2° prophylaxis after prior FN w/ lower-intensity chemo
- EPO (α, β, darbepoetin): CKD, cancer (w/ chemo), zidovudine
- TPO-RAs (romiplostim, eltrombopag): ITP, aplastic anemia, hemorrhage prevention
- TPO = critical stem cell growth factor; investigational for CAR-T cytopenia
5.1 Introduction
- Hematopoietic GFs (HGFs): promote survival, proliferation, differentiation of BM precursors
- Major: G-CSF, GM-CSF, SCF, EPO, TPO
- Bind cognate HGFR → JAK-STAT & MAPK pathways
- Regulatory approval: equivalent safety/efficacy to originator; amino acid ↔︎ allowed if structure/function preserved
5.2 Myeloid Growth Factors
5.2.1 Granulocyte Colony-Stimulating Factor (G-CSF)
Clinical Use: - 1st-line myeloid GF - G-CSF binds G-CSF receptor → neutrophil progenitor survival, proliferation, maturation - Primary use: ↓ chemo-induced febrile neutropenia (FN)
| Indication | Details |
|---|---|
| 1° prophylaxis, chemo FN | Myeloablative/dose-intense chemo; post-induction AML |
| PBSC mobilization | Allogeneic SCT from normal donors |
| Severe chronic neutropenia | Congenital, acquired, idiopathic; response documented |
Primary Prophylaxis (FN Prevention): - Definition FN: temp >38.3°C w/ neutrophils <0.5 × 10⁹/L during chemo - Guidelines mandate G-CSF for anticipated FN risk >20% - Randomized trials: ↓ FN rates, improved outcomes - Dosing: G-CSF 5 mcg/kg/d SC × 10d post-chemo - OR pegfilgrastim 6 mg SC once per cycle
Pegfilgrastim (Peg-CSF): - Pegylated product: sustained G-CSF activity w/ single dose - Overcomes short half-life (~4h) of native G-CSF - 6 mg SC ≥24h after chemo - Superior to native G-CSF: ↓ FN, ↓ neutropenia duration - Same FDA indications as G-CSF
Secondary Prophylaxis: - After prior neutropenia/FN event if further chemo needed - Peg-CSF for less intensive regimens if risk ↓ significantly
PBSC Mobilization: - ↑ PBSC recovery & neutrophil recovery post-autologous HSC transplant - Start G-CSF ≥2d before leukapheresis; continue until mobilization complete
Severe Chronic Neutropenia: - Definition: persistent ANC <0.5 × 10⁹/L w/ recurrent bacterial infections - Organisms: Staph aureus, Klebsiella, Burkholderia, fungal (Aspergillus, Serratia, Nocardia) - Genetics: autosomal dominant/recessive forms - G-CSF effect: ↑ ANC (doses 3–600 mcg/kg/d), ↓ infection risk - Risk: prolonged use a/w MDS, AML, monosomy 7 (>10% incidence in chronic cohorts)
G-CSF effective for FN prevention & chronic neutropenia. Requires monitoring for monosomy 7, MDS, leukemia w/ chronic use. Long-term surveillance essential.
Clinical Outcomes: - ↓ FN duration, hospital admissions - Toxicities: allergic rxn, arthralgias, myalgias, splenic rupture (rare), ARDS, ↑ MDS/AML risk
Guidelines: 1. 1° prophylaxis: high-risk (>20% FN) chemo patients 2. 1° prophylaxis: dose-intense regimens 3. 2° prophylaxis: after FN in subsequent chemo 4. Avoid w/ radiotherapy/nuclear incident 5. Use clinical judgment for discretionary cases
5.2.2 Granulocyte-Macrophage CSF (Sargramostim)
Biology: - Synergistic w/ G-CSF for myelopoiesis - Source: T cells, macrophages, endothelial cells, fibroblasts - Effect: ↑ circulating neutrophils, maturation, function; ↑ antigen presentation
| Indication | Details |
|---|---|
| Post-BMT myeloid recovery (allo/auto) | Improve engraftment, ↓ mortality & infection |
| PBSC mobilization | Enhance collection via leukapheresis |
| AML (age >2y) | Accelerate myeloid recovery, ↑ DFS |
Post-Transplant Myeloid Recovery: - ↓ time to neutrophil recovery vs standard care - Similar effect to G-CSF; may enhance progenitor mobilization
Sargramostim Forms: - Only recombinant form (differs from native by single AA at position 23) - IV dosing per randomized trials
Clinical Use: - Less common than G-CSF due to AE profile - Option for post-BMT rapid recovery w/ high-dose chemo
5.2.3 GM-CSF for FN Prevention
- Approved for transplantation/mobilization, NOT primary FN prophylaxis
- FN risk >20%: limited RCT evidence vs G-CSF (standard)
- Rarely used for solid tumor chemo FN prevention
5.2.4 Treatment of Febrile Neutropenia
- All FN patients: empiric antibiotics; culture before ABX
- G-CSF > GM-CSF in meta-analyses for FN reduction & severity
- Current NCCN: GF accelerates ANC recovery, limited ↓ LOS
- NOT routinely used post-ABX w/o documented benefit
- Peg-CSF ↑ recovery & ↓ need for repeat dosing vs native G-CSF
5.2.5 Acute Myeloid Leukemia
- 7 RCTs: NO consistent benefit of G-CSF on infection, LOS, overall outcomes
- NOT recommended for routine use
5.2.6 PBSC Mobilization & Neutrophil Recovery Post-Autologous Transplant
- PBSC preferred over BM: ease of collection, ↓ graft failure, rapid recovery
- G-CSF/GM-CSF: ↑ CD34+ cell recovery, ↑ neutrophil recovery post-autologous HSC transplant
- TPO: investigational for stem cell expansion & mobilization
5.2.7 Delayed Engraftment or Graft Failure Post-BMT or CAR-T
- Patients w/ ANC <0.5 × 10⁹/L or ↓ baseline
- Uncontrolled data: GM-CSF ↓ time to recovery
- No RCT evidence; use a/w ↓ GVHD, poor mobilization, serious infections
5.2.8 Severe Chronic Neutropenia (Idiopathic, Cyclic, Congenital)
- Definition: ANC <0.5 × 10⁹/L persistently w/ recurrent infections
- G-CSF: dose 3–600 mcg/kg/d; ↑ ANC, ↓ infection severity
- Long-term monitoring: ↑ leukemia/MDS risk (>10% w/ prolonged use)
5.2.9 Acute Lymphoblastic Leukemia
- 8 RCTs (>7000 patients): NO benefit of G-CSF on infection, LOS, overall outcomes
- NOT recommended for routine use
5.2.10 PBSC Mobilization & Neutrophil Recovery in ALL
- PBSC preferred: ↓ graft failure, rapid ANC recovery
- BM: non-malignant disorders (graft-vs-cancer effect)
- 18 trial meta-analysis (n=1198): PBSC post-autologous SCT = BM on acute/chronic GVHD risk
5.3 Erythroid Growth Factors
5.3.1 Erythropoietin
Biology: - EPO: primary regulator of RBC production - Source: fetal liver; adult: renal interstitial fibroblasts (HIF-1α sensing) - Mechanism: EPO→EPOR → downstream signaling → erythroid progenitor proliferation, maturation, differentiation - Loss of signaling: severe anemia, embryonic death - Terminal differentiation: requires EPO for CFU-E colonies
FDA-Approved Uses:
| Indication | Details |
|---|---|
| CKD | Normocytic anemia a/w EPO ↓; goal Hgb <10 g/dL |
| Cancer w/ chemo | Anemia from chemo; FDA warning: ↑ VTE, MI, stroke |
| Zidovudine (AZT) | HIV anemia; ↑ Hgb, eliminates transfusions |
Chronic Kidney Disease: - Normocytic anemia in majority of CKD → ESRD - Goal Hgb: lowest to avoid transfusion, ≤10 g/dL - Initial dose: epoetin-α 50 U/kg SC 3×/wk or IV; OR 40,000 U/wk SC - Target: Hgb 10–11 g/dL - Titration: maintain physiologic range; ↓ if HTN or polycythemia - Monitoring: weekly during titration, then q8wks - Iron: oral/parenteral replacement ↑ response if ferritin <30 ng/mL, TSAT <20%, or functional ferritin <100 ng/mL - Dialysis: once/wk dosing tolerated; 4000 U/wk alternative
ASH/ASCO/NCCN Guidelines: - Exclude reversible anemia causes - Aggressive iron replacement; goal Hgb <10 g/dL - ESA caution: ↑ VTE, MI, stroke risk - Consider transfusion preferentially in high-risk patients - Suspend EPO if new thrombotic event/stroke
Cancer w/ Chemotherapy: - Limited ESA data; FDA warning: ↑ thrombotic risk - Target Hgb <10 g/dL to minimize complications - Blood pressure monitoring essential
EPO ↑ VTE risk in cancer; target Hgb <10 g/dL. Monitor BP during therapy.
Other Uses (Limited Data): - Perioperative anemia: blood-conserving techniques, delayed transfusion - Allogeneic transfusion avoidance: limited evidence; dose-dependent ↑ thrombotic risk - HIV-associated anemia: rare w/ effective ART; prior zidovudine/ganciclovir/infections contribute - hEPO effective if baseline Hgb <9%, responds to 10,000 U/wk regimen
Adverse Effects: - Cardiovascular: HTN exacerbation, MI, CHF, stroke - VTE, thromboembolism - Pure RBC aplasia: anti-EPO antibody development (reportable) - Target low Hgb (<10 g/dL) to mitigate CV risk
5.4 Platelet Growth Factors
5.4.1 Thrombopoietin & TPO Receptor Agonists
Biology: - TPO: major regulator of megakaryopoiesis & platelet production - Also critical stem cell growth factor - TPO receptor (MPL) signaling → JAK-STAT, MAPK → anti-apoptotic effects - Gene: chromosome 3; mutations → thrombocytosis or thrombocytopenia
TPO Receptor Agonists (TPO-RAs): - FDA-approved: romiplostim (SC), eltrombopag (oral) - Romiplostim: FC-conjugated; stimulates platelet production via MPL binding - Dosing: 1–3 mcg/kg SC weekly; max 10 mcg/kg - Adjust weekly per platelet response - Eltrombopag: non-peptide small molecule mimetic - Oral TPO-RA; promotes megakaryocyte growth & platelet production
Clinical Indications:
| Setting | Use |
|---|---|
| ITP | 1st-line approved indication |
| Aplastic anemia | Severe aplastic anemia, platelet recovery support |
| Post-transplant thrombocytopenia | Prolonged isolated thrombocytopenia; 2° platelet recovery failure |
| Chronic liver disease | Pre-procedure platelet correction; start ~1 wk prior |
| CAR-T cytopenia | Investigational; rational extension of stem cell support |
Dose & Monitoring: - Romiplostim preferred per NCCN & ISTH for ↑ response & complete hematologic recovery - Start 1–3 mcg/kg; titrate weekly to goal platelet count - Chronic liver disease: eltrombopag used for hepatitis C-related cirrhosis antiviral support
Precautions: - TPO-RAs indispensable for stem cell growth in vitro - Use for thrombocytopenia & stem cell insufficiency post-transplant rational - Prior liberal hEPO adoption cautions: monitor for adverse cancer outcomes - Evidence expanding in aplastic anemia, CAR-T toxicity, post-transplant settings
Transfusion Thresholds (NCCN/ISTH): - Prophylactic transfusion: plt <10 × 10⁹/L - Severe bleeding: even w/ plt ≥50 × 10⁹/L - Preferred strategy: enroll in TPO-RA clinical trial if available - If unavailable: dose delays (especially full-dose chemo expected to be more clinically relevant)