Neuroblastoma
Contents (8)
Neuroblastoma is a malignant tumor arising from neural crest cells of the sympathetic nervous system, representing the most common extracranial solid malignancy in children. It accounts for approximately 6-10% of all pediatric cancers, with an incidence of 1 in 7,000 live births, typically presenting in children under 5 years of age. The disease demonstrates remarkable biologic heterogeneity, ranging from spontaneous regression in infants to highly aggressive presentations requiring intensive multimodal therapy. Clinical significance is magnified by the unpredictable natural history—some tumors undergo spontaneous maturation or regression while others progress rapidly despite treatment, making neuroblastoma a paradigm for understanding pediatric cancer biology. Neuroblastoma is essential for USMLE Step 2 CK preparation due to its frequency as a board question topic, unique prognostic factors, and management nuances distinct from other pediatric malignancies.
Developmental origin and differentiation spectrum
Neuroblastoma arises from neural crest-derived sympathoadrenal precursor cells that normally migrate during embryogenesis (weeks 5-12) to form the adrenal medulla and sympathetic ganglia. The disease exists along a continuum of differentiation: undifferentiated neuroblastoma (worst prognosis) → intermediate differentiation → ganglioneuroblastoma (mixed) → ganglioneuroma (benign, fully differentiated). This spectrum directly influences outcome—differentiated tumors have significantly better prognosis. Dysregulation of normal developmental apoptosis and differentiation programs allows transformation of these otherwise transient cell populations. The tumor's location reflects the distribution of sympathoadrenal tissue: 40% arise in the adrenal medulla, 25% in abdominal paraspinal ganglia, 15% in thoracic locations, and 20% in other sites (pelvis, neck, mediastinum).
Molecular oncogenesis—MYCN amplification and pathway dysregulation
The most critical molecular driver is MYCN proto-oncogene amplification, occurring in 20-25% of cases and representing the single strongest negative prognostic factor. MYCN (amplified in neuroblastoma) is a transcription factor of the MYC family that drives:
- Uncontrolled cell proliferation through increased G1/S transition
- Inhibition of differentiation pathways (particularly retinoic acid-responsive genes)
- Enhanced metabolic activity and genomic instability
- Transcriptional activation of genes promoting angiogenesis and metastasis
High MYCN expression (>10-fold amplification) confers 5-year survival rates of <10% compared to >90% in MYCN non-amplified tumors. MYCN amplification often correlates with segmental chromosomal abnormalities (losses of chromosomes 1p and 11q) rather than the favorable whole-chromosome gains seen in low-risk disease.
Favorable genetic alterations
In contrast, whole-chromosome gains (particularly trisomy 17, trisomy 18, hyperploidy with 47+ chromosomes) indicate superior prognosis through mechanisms that may include cellular stress responses and reduced genomic instability. These genetic patterns are found almost exclusively in infants and young children with localized, low-risk disease. DNA ploidy status (near-diploid vs. hyperdiploid) serves as an independent prognostic marker, with hyperdiploidy associated with better outcomes.
Neurotrophin and cell adhesion pathways
Reduced expression of p75 neurotrophin receptor (a tumor suppressor promoting differentiation and apoptosis) and increased TrkA tyrosine kinase receptor expression paradoxically indicate better prognosis—these tumors remain responsive to nerve growth factor (NGF)-mediated differentiation signals. Conversely, elevated TrkB expression (associated with MYCN amplification) indicates worse prognosis and resistance to differentiation therapy. Loss of tumor suppressor genes (TP53, PTEN, CHD5) and gain-of-function mutations in ATRX, ALK, and PHOX2B further promote aggressive phenotypes.
Catecholamine metabolism and sympathomimetic effects
Neuroblastoma tumors synthesize and metabolize norepinephrine and dopamine via the sympathetic nervous system pathway. Breakdown of these catecholamines produces metanephrines, normetanephrine, vanillylmandelic acid (VMA), and homovanillic acid (HVA), which are markedly elevated in urine and serum of most patients (>90% sensitivity). These metabolites can produce paraneoplastic symptoms including hypertension, flushing, and diaphoresis, though true pheochromocytoma-like crises are uncommon. Measurement of urine metanephrines serves dual purposes: diagnostic biomarker and correlate of tumor burden.
Angiogenesis and tumor microenvironment
Neuroblastoma demonstrates remarkable heterogeneity in vascularization, from poorly vascularized masses to highly angiogenic tumors. VEGF (vascular endothelial growth factor) and related pathways drive tumor neovascularization, enabling rapid growth. The permissive microenvironment includes immunomodulatory effects where tumors escape immune surveillance through TGF-β signaling and production of immunosuppressive mediators. This immunologic dysfunction is mechanistically linked to MYCN amplification and undifferentiated phenotypes.
Genetic predisposition syndromes
- PHOX2B mutations (2-3% of neuroblastoma): Autosomal dominant germline mutations in this developmental transcription factor cause hereditary predisposition to neuroblastoma and represent the major identified genetic susceptibility factor. Associated with earlier presentation, often bilateral adrenal involvement, and increased risk of secondary malignancies. Families with PHOX2B mutations require surveillance imaging.
- ALK mutations (6-10% of familial cases, 1-2% of sporadic): Gain-of-function mutations in anaplastic lymphoma kinase (a receptor tyrosine kinase) predispose to neuroblastoma, typically with earlier presentation and sometimes multifocal disease. ALK mutations may be acquired (somatic) or inherited (germline).
- Familial predisposition without identified mutations: ~5% of neuroblastoma cases occur in familial clusters without defined germline mutations, suggesting additional susceptibility loci.
Chromosomal and syndromic associations
- Down syndrome (Trisomy 21): ~10-fold increased neuroblastoma risk; mechanisms unclear but may relate to gene dosage effects of chromosome 21 genes in neural crest development.
- Beckwith-Wiedemann syndrome, WAGR syndrome, Denys-Drash syndrome: Associated with increased abdominal malignancy risk including neuroblastoma through TP53 and IGF2 pathway dysfunction.
- Neurofibromatosis Type 1: Slight increased risk; NF1 protein (neurofibromin) acts as RAS inhibitor, and loss promotes transformation.
Developmental and environmental factors
- Maternal estrogen exposure: Conflicting data regarding maternal hormone use, but some studies suggest association with neuroblastoma.
- Parental occupational exposures: Potential associations with paternal agricultural/pesticide exposure remain unconfirmed.
- Maternal diabetes and obesity: Emerging evidence suggests maternal metabolic conditions may increase risk, possibly through growth factor dysregulation.
Age and development
The critical window for neuroblastoma development is in utero and early infancy, corresponding to the physiologic migration period of neural crest cells. This explains why virtually all neuroblastomas present before age 10, with median age at diagnosis of 18-24 months. The rarity of neuroblastoma in children >10 years suggests either selection pressure against older presentation or incomplete transformation of later-developing precursor lesions. Notably, in utero screening studies have demonstrated neuroblastoma precursor lesions (neuroblastomatosis) in ~1 in 100 infant autopsies, yet clinical disease occurs in only 1 in 7,000 births, supporting the hypothesis of spontaneous regression in many cases—a unique biologic phenomenon in pediatric oncology.
Presentation by stage and tumor location
The clinical presentation of neuroblastoma is highly variable and depends critically on tumor location, degree of MYCN amplification, and whether presentation is primary disease or metastatic. Approximately 50% of children present with localized disease, 25% with regional extension, and 25% with metastatic disease at diagnosis.
Abdominal mass (most common primary manifestation)
The most frequent presentation is an asymptomatic abdominal mass discovered incidentally on physical examination or imaging obtained for unrelated reasons. Adrenal and paraspinal neuroblastomas present as firm, fixed flank or epigastric masses. Parents often note an enlarging abdominal distention or report palpating a mass during diaper changes. Large primary tumors can cause:
- Intestinal obstruction or displacement (abdominal distention, constipation)
- Splenic or hepatic displacement
- Hydronephrosis from ureteral compression
- Inferior vena cava compression (rare)
Thoracic presentations
Mediastinal and thoracic paraspinal neuroblastomas are often discovered on chest X-ray obtained for other indications (respiratory infection, routine evaluation). These tumors may compress the trachea or esophagus. Importantly, thoracic neuroblastomas have more favorable biologic characteristics and better overall survival (>80%) compared to abdominal tumors, particularly in younger children.
Constitutional and paraneoplastic symptoms
- Fever, weight loss, and failure to thrive: Represent systemic effects of tumor burden and cytokine production (IL-6, TNF-α); notably, these symptoms may indicate aggressive disease.
- Hypertension: Occurs in 5-10% of cases due to catecholamine excess; typically moderate elevations (110-130 systolic) rather than hypertensive crises. Diarrhea from VIP or other peptide secretion is rare but pathognomonic when present.
- Opsoclonus-myoclonus-ataxia (OMA) syndrome: A paraneoplastic neurologic syndrome occurring in 2-4% of cases, characterized by rapid, chaotic eye movements (opsoclonus), myoclonic jerks, ataxia, and behavioral changes. Mediated by tumor-directed autoimmune response (anti-CRMP5 antibodies). Despite neurologic severity, OMA is associated with favorable prognosis and localized, low-risk disease—this counter-intuitive association is a classic board point. OMA may antedate tumor detection and occasionally persists after successful tumor treatment.
Metastatic disease presentations
- Bone metastases (60% of metastatic cases): Typically metaphyseal lesions causing bone pain and limping. Long bone or vertebral involvement presents with pain out of proportion to imaging findings or with acute neurologic symptoms.
- Bone marrow involvement: Causes anemia, thrombocytopenia (bleeding, petechiae), and neutropenia (infections). The combination of anemia, thrombocytopenia, and hepatosplenomegaly in an infant can mimic leukemia ("neuroblastoma in leukemia distribution").
- Liver metastases: Massive hepatomegaly with relatively preserved synthetic function distinguishes neuroblastoma from hepatoblastoma. In infants (Stage 4S disease, see below), remarkable hepatomegaly may occur with preserved liver function.
- Lymph node metastases: Regional nodes (retroperitoneal for abdominal primary) or distant nodes (mediastinal, supraclavicular).
- Skin and subcutaneous metastases: Rare but characteristic "blueberry muffin" appearance in infants with metastatic disease (due to dermal nodules and blanching erythema).
- CNS metastases: Uncommon (<5% at diagnosis) but may occur with aggressive disease; intracranial deposits can present with symptoms of raised intracranial pressure.
Physical examination findings
- Abdominal mass: Firm, fixed, non-tender mass crossing midline (distinguishing from other abdominal tumors)
- Hepatomegaly: Hard, irregular liver edge; degree correlates with metastatic burden
- Lymphadenopathy: Regional and distant node enlargement
- Skeletal deformities or limited mobility: From bone metastases
- Neurologic signs: Weakness, ataxia, hyper-reflexia from spinal involvement or paraneoplastic syndrome
- Hypertension: Measured blood pressure elevated for age
- Skin lesions: Nodules, erythema, "blueberry muffin" appearance in metastatic disease
- Eye findings in OMA: Opsoclonus, nystagmus, skew deviation
Age-specific presentations
Infants and very young children (age <1-2 years) are most likely to have low-risk, localized disease or present with the special Stage 4S category (see Diagnosis section), characterized by rapid hepatomegaly but relatively indolent course. Children >5 years more commonly present with advanced disease and unfavorable biology, though their overall prognosis may be better with modern intensive therapy. Adolescents with neuroblastoma (rare) typically have MYCN-amplified, highly aggressive disease with very poor prognosis.
Clinical suspicion and initial evaluation
Neuroblastoma should be suspected in any child <5 years (especially <2 years) with:
- Abdominal mass or abdominal distention
- Unexplained anemia, thrombocytopenia, or cytopenias
- Bone pain or limping without clear trauma
- Constitutional symptoms (fever, weight loss)
- Hypertension in infancy/early childhood
- Opsoclonus-myoclonus-ataxia syndrome
Initial evaluation includes detailed history of symptom onset, family history of cancer or neuroblastoma, prenatal and perinatal events, and thorough physical examination with particular attention to abdominal palpation, vital signs (blood pressure), neurologic examination, and skin inspection.
Biochemical markers and laboratory tests
Urine metanephrines and catecholamine metabolites
- 24-hour urine metanephrines, normetanephrines, VMA, and HVA: Elevated in >90% of neuroblastoma cases; highly sensitive but not specific for neuroblastoma (elevated in pheochromocytoma, some cases of hypertension). VMA (vanillylmandelic acid) and HVA (homovanillic acid) are alternative markers. Ratios of HVA/VMA may provide some prognostic information (HVA>VMA associated with worse prognosis in some studies).
- Normal values vary by age and laboratory but generally: VMA <7 mg/24h, HVA <8 mg/24h, metanephrines <0.5 μg/kg/24h
Serum biomarkers
- Neuron-specific enolase (NSE): Elevated in 75-85% of cases; prognostic marker with very high levels (>160 ng/mL) associated with worse prognosis; not specific.
- Serum ferritin: Elevated in 80% of cases; highest levels in advanced disease and MYCN-amplified tumors; prognostic indicator (>143 ng/mL associated with worse outcomes).
- Lactate dehydrogenase (LDH): Elevated in proportion to tumor burden; LDH >900 U/L indicates worse prognosis; used in risk stratification.
- Chromogranin A: Elevated in some cases but less commonly used for diagnosis.
- Glycolipid GD2: Expressed on neuroblastoma cell surface; used for immunotherapy but not a diagnostic test.
Complete blood count: Assess for anemia (from marrow involvement or chronic disease), thrombocytopenia, and neutropenia; may mimic leukemia if significant marrow infiltration.
Metabolic panel: LFTs may show mild elevation; renal function assessment important for therapy planning; coagulopathy assessment if advanced disease.
Imaging studies—diagnostic and staging
Contrast-enhanced CT of the abdomen and pelvis
Gold standard for localizing primary tumor and assessing local extension. Features of neuroblastoma include:
- Heterogeneous mass with areas of necrosis
- Enhancement post-contrast (though less than adrenal adenoma)
- Calcifications (50% of cases)—"comma-shaped" or stippled pattern is characteristic
- Mass crossing midline (typical of paraspinal location)
- Displacement of adjacent organs
- Involvement of adjacent structures
CT assesses resectability at diagnosis (distinguishes Stage 2A from 2B based on imaging findings).
Chest X-ray and CT chest
Essential for detecting mediastinal/thoracic primary tumors and evaluating for pulmonary metastases. Thoracic tumors appear as well-defined
Immediate stabilization (before oncologic therapy)
- Symptomatic spinal cord compression (dumbbell tumor through a neural foramen): a neuro-oncologic emergency. Corticosteroids (dexamethasone) plus urgent chemotherapy is generally favored over emergency laminectomy in children because laminectomy risks progressive kyphoscoliosis; Children's Oncology Group (COG) protocols and NCCN neuroblastoma guidance emphasize chemotherapy-first for chemosensitive disease.
- Stage MS/4S with massive hepatomegaly in an infant: hepatic enlargement can cause respiratory failure, renal vein compression, and abdominal compartment syndrome. Low-dose chemotherapy or low-dose hepatic radiation is used to buy time until spontaneous regression occurs.
- Catecholamine-mediated hypertension: treat with alpha blockade before any beta blockade, as in pheochromocytoma, to avoid unopposed alpha vasoconstriction.
Risk-stratified therapy (COG/International Neuroblastoma Risk Group system — stage, age, MYCN status, histology, ploidy, 11q)
- Low risk: surgical resection alone, or observation only for perinatally detected small adrenal masses and for asymptomatic stage MS/4S infants, exploiting spontaneous regression.
- Intermediate risk: moderate-intensity multiagent chemotherapy — platinum (carboplatin), alkylator (cyclophosphamide), anthracycline (doxorubicin), and topoisomerase II inhibitor (etoposide) — followed by delayed resection. Therapy is de-escalated in favorable-biology tumors.
- High risk: three-phase regimen per COG. Induction with dose-intensive chemotherapy (including topotecan/cyclophosphamide, cisplatin/etoposide) plus resection of the primary; consolidation with high-dose chemotherapy and autologous hematopoietic stem cell rescue plus radiation to the primary site; post-consolidation maintenance with isotretinoin (13-*cis*-retinoic acid, a differentiating agent) combined with the anti-GD2 monoclonal antibody dinutuximab plus GM-CSF and interleukin-2.
Relapsed/refractory options
- ALK tyrosine kinase inhibitors (lorlatinib, crizotinib) for ALK-mutated tumors; ¹³¹I-MIBG therapy; re-induction chemotherapy; additional anti-GD2 antibody therapy.
Avoid
- Aggressive resection in low-risk/MS disease — morbidity exceeds benefit given regression potential.
- Isotretinoin in a pregnant caregiver or adolescent patient without contraception — potent teratogen.
- Live vaccines and unshielded blood products during immunosuppressive therapy (use irradiated, leukoreduced products).
Disease-related — emergencies
- Epidural spinal cord compression: paraspinal tumor grows through the intervertebral foramen (dumbbell/hourglass tumor). Signaled by new lower-extremity weakness, hyperreflexia, urinary retention, or refusal to walk. Emergent MRI of the entire spine; steroids and urgent chemotherapy.
- Respiratory failure from hepatomegaly in stage MS/4S: rapidly expanding liver splints the diaphragm and raises intra-abdominal pressure, causing tachypnea, oliguria, and lower-extremity edema.
- Tumor lysis syndrome: bulky chemosensitive disease releases intracellular contents — hyperkalemia, hyperphosphatemia, hyperuricemia, hypocalcemia, and acute kidney injury. Hydration and rasburicase/allopurinol.
- Febrile neutropenia: marrow infiltration plus myelosuppressive therapy; requires immediate empiric broad-spectrum antipseudomonal beta-lactam therapy.
- Cervical/apical thoracic tumor with airway compromise, and Horner syndrome (ptosis, miosis, anhidrosis) from sympathetic chain involvement.
Disease-related — non-emergent
- Marrow failure: anemia, thrombocytopenia, and bone pain from metastatic infiltration; may masquerade as leukemia.
- Secretory diarrhea from VIP production (ganglioneuroblastoma) causing hypokalemia and dehydration.
- Opsoclonus-myoclonus-ataxia: immune-mediated; residual cognitive, language, and motor deficits persist in many children even after tumor cure.
Treatment-related
- Anthracycline cardiomyopathy: free-radical and topoisomerase IIβ-mediated myocyte injury; falling ejection fraction on surveillance echocardiography, cumulative-dose dependent.
- Cisplatin ototoxicity and nephrotoxicity: outer hair cell death gives high-frequency sensorineural hearing loss (critical in a toddler acquiring language); renal magnesium wasting.
- Cyclophosphamide/ifosfamide: hemorrhagic cystitis from acrolein (prevented with mesna and hydration) and gonadal failure.
- Dinutuximab: GD2 is expressed on peripheral nerves, so infusion causes severe neuropathic pain requiring scheduled opioids; also capillary leak syndrome and hypotension.
- Isotretinoin: mucocutaneous dryness, hypertriglyceridemia, pseudotumor cerebri.
- ¹³¹I-MIBG: hypothyroidism unless thyroid is blocked with potassium iodide; prolonged myelosuppression.
- Late effects: second malignancies (AML/MDS from alkylators and topoisomerase II inhibitors), growth failure, scoliosis in the radiation field, and endocrinopathy.
- The single best next step in a toddler with a firm abdominal mass: urinary catecholamine metabolites (VMA and HVA) with cross-sectional imaging; tissue diagnosis and bilateral bone marrow aspirates/biopsies plus MIBG scintigraphy complete staging. Do not order urine catecholamines after starting therapy.
- Neuroblastoma vs Wilms tumor is the classic distractor pair. Neuroblastoma crosses the midline, encases (rather than displaces) vessels, is calcified on CT, and causes elevated VMA/HVA. Wilms is smooth, confined to one side, presents with hematuria and hypertension from renin, and displaces vessels.
- MYCN amplification is the association examiners test: it defines high-risk disease regardless of age or stage and drives the intensive induction–transplant–immunotherapy pathway.
- Histology buzzword: small round blue cell tumor with Homer Wright pseudorosettes (neuroblasts around a neuropil core) and a background of neurofibrillary material.
- Periorbital ecchymoses with proptosis (raccoon eyes) from sphenoid/orbital metastasis is a classic stem — the trap answer is non-accidental trauma. A blueberry muffin infant with skin nodules and hepatomegaly is the other classic image.
- Opsoclonus-myoclonus-ataxia (dancing eyes, dancing feet) is paraneoplastic and, counterintuitively, marks localized, favorable-biology disease — yet neurodevelopmental sequelae often persist.
- Stage MS/4S in an infant (localized primary with skin, liver, and limited marrow spread) may be observed because of spontaneous regression; treating everything aggressively is the wrong answer unless the liver is causing respiratory or renal compromise.
- Favorable prognostic features: age under 18 months, hyperdiploidy, whole-chromosome gains, differentiated histology, high TrkA. Unfavorable: MYCN amplification, 1p and 11q loss, near-diploidy, high TrkB, elevated LDH/ferritin.
- Dinutuximab causes severe neuropathic pain because GD2 sits on peripheral nerves — anticipate opioids, not an allergic-reaction answer.