Neuroblastoma

Introduction And Epidemiology

• Most common extracranial solid tumor in children.
• Accounts for 6-10% of all childhood malignancies.
• Most commonly diagnosed malignancy in first year of life.
• Annual incidence: 10 per million live births.
• Median age at diagnosis: 18-19 months.
• Age distribution: 50% under 2 years, 75% under 4 years, 90% under 10 years.
• Peak incidence occurs at 2 years of age.
• Originates from primordial neural crest cells destined for adrenal medulla and sympathetic ganglia.
• Slight male and White population preponderance.
• Spontaneous involution or maturation occurs frequently; in situ neuroblastoma detected in 1 in 259 infant autopsies.

Etiology And Pathogenesis

Genetics And Chromosomal Abnormalities

• Etiology largely unknown.
• Familial cases represent 1-2%; associated with younger diagnostic age.
• Germline gain-of-function variants in ALK gene linked to familial neuroblastoma.
• Germline pathogenic variants in PHOX2B predispose to syndromic neuroblastoma.
• BARD1 gene identified as major genetic contributor.
• MYCN proto-oncogene amplification detected in 20% of primary tumors; strongly predicts advanced stage and poor prognosis.
• Segmental chromosomal aberrations (SCA) confer increased recurrence risk: loss of heterozygosity of 1p, 11q, 14q; gain of 17q,.
• Hyperdiploid tumor DNA content associated with favorable outcome in infants under 18 months without MYCN amplification.
• Diploid DNA content predicts less favorable outcome.
• Whole genome sequencing identifies additional loss of function in ATRX and TERT.

Associated Syndromes

Syndrome Category	Specific Disorders
Neurocristopathy Syndromes	Hirschsprung disease, Congenital central hypoventilation syndrome (PHOX2B variant),.
Overgrowth Syndromes	Beckwith-Wiedemann syndrome, Hemihypertrophy.
RASopathies	Neurofibromatosis type I, Noonan syndrome, Costello syndrome.
Other Inherited Disorders	Turner syndrome, Fanconi anemia, Familial pheochromocytoma/paraganglioma, Li-Fraumeni syndrome,.
Environmental/Maternal	Fetal alcohol syndrome, fetal hydantoin syndrome.

Pathology And Cellular Characteristics

• Extremely undifferentiated small round blue cell tumors to mature Schwannian stroma with ganglion cells.
• Characteristic histopathologic feature: Homer-Wright pseudorosettes (circular groupings of dark tumor cells surrounding pale neurofibrils).

Immunohistochemical Profile

Marker Type	Findings
Positive Markers	Synaptophysin, tyrosine hydroxylase, PHOX2B, neuron-specific enolase (NSE), NB84.
Negative Markers	Hematopoietic markers (CD45), desmin, myogenin, keratin, CD99.

Note: PHOX2B exhibits high specificity and sensitivity for neuroblastic tumors.

Clinical Manifestations

Anatomical Distribution And Local Symptoms

• Metastasizes via local invasion or distant hematogenous/lymphatic routes.
• Distant metastases present at diagnosis in 75% of cases.

Primary Site	Frequency	Clinical Manifestations
Abdomen	65% (46% Adrenal, 19% Paraspinal)	Asymptomatic palpable mass, abdominal distension, pain, renovascular hypertension.
Posterior Mediastinum	25%	Dyspnea, dysphagia, pulmonary infections, lymphatic compression, stridor,.
Pelvis	4%	Genitourinary obstruction, constipation.
Head And Neck	3%	Palpable neck mass.

Specific Clinical Syndromes

Syndrome	Clinical Features And Pathophysiology
Horner Syndrome	Unilateral ptosis, miosis, anhidrosis; secondary to cervical or upper thoracic sympathetic compression.
Opsoclonus-Myoclonus-Ataxia (Dancing Eyes)	Myoclonic jerking, random conjugate eye movements, cerebellar ataxia; autoimmune paraneoplastic origin; often associated with biologically favorable tumors.
Kerner-Morrison Syndrome	Intractable secretory watery diarrhea and hypokalemia; caused by tumor secretion of vasoactive intestinal peptide (VIP).
Hutchinson Syndrome	Limping, irritability, bone pain; represents diffuse bone and bone marrow metastases.
Pepper Syndrome	Massive hepatomegaly with or without respiratory distress; characterizes Stage MS disease in infants.

Diagnostic Evaluation

• Biochemical Markers: Elevated urinary catecholamine metabolites (homovanillic acid [HVA], vanillylmandelic acid [VMA]) detected in 95% of cases.
• Bone Marrow Evaluation: Bilateral aspirates and biopsies required. Diagnosis confirmed without primary tumor biopsy if marrow exhibits small round blue cells (rosettes) concurrently with elevated urinary catecholamines.
• Anatomical Imaging: Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) evaluates primary tumor extent. MRI strictly preferred for paraspinal lesions (assesses cord compression) and neck masses.
• Functional Imaging: 123I-MIBG (meta-iodobenzylguanidine) scintigraphy detects 90% of neuroblastomas; evaluates bone and soft tissue metastases. 18F-FDG PET utilized for MIBG-nonavid tumors.

Staging Systems

Historical use of International Neuroblastoma Staging System (INSS) replaced by image-based International Neuroblastoma Risk Group Staging System (INRGSS).

International Neuroblastoma Risk Group Staging System (INRGSS)

Stage	Definition
L1	Localized tumor confined to one body compartment; lacks Image-Defined Risk Factors (IDRFs).
L2	Locoregional tumor demonstrating locally invasive features; presence of one or more IDRFs.
M	Distant metastatic disease (bone, bone marrow, liver, distant lymph nodes, other organs).
MS	Metastatic disease in children <18 months; metastases strictly confined to skin, liver, and/or bone marrow (<10% marrow involvement); lacks bone involvement.

Prognostic Factors And Risk Stratification

Prognosis strongly dictated by clinical and biologic characteristics.

Prognostic Factor	Favorable Profile	Unfavorable Profile
Age At Diagnosis	<18 months	$\ge$ 18 months.
Stage (INRGSS)	L1, L2, MS	M.
MYCN Status	Nonamplified	Amplified.
Tumor Ploidy (DNA Index)	Hyperdiploid (in infants)	Diploid.
Histology (INPC)	Differentiated; Low/Intermediate MKI	Undifferentiated; High MKI.
Chromosomal Aberrations	Absent	Present (LOH 1p, 11q; Gain 17q).

Management And Therapeutics

Therapy risk-adapted incorporating age, stage, and molecular features.

Low-Risk Disease

• Encompasses Stage L1, select L2, and asymptomatic Stage MS.
• Primary Therapy: Surgical resection (L1/L2) or expectant observation (MS).
• Survival exceeds 90% without systemic therapy.
• Chemotherapy/Radiation reserved strictly for symptomatic life-threatening hepatomegaly (Pepper syndrome) in infants causing respiratory compromise.

Intermediate-Risk Disease

• Encompasses symptomatic <18 months L2, >18 months L2 with favorable biology, and infants (<12-18 months) with Stage M demonstrating favorable biology.
• Systemic Therapy: Moderate-dose multiagent chemotherapy. Regimen includes Carboplatin, Etoposide, Cyclophosphamide, and Doxorubicin.
• Therapeutic Goal: Achievement of partial response (>50% tumor volume reduction); complete resolution unnecessary.
• Surgery: Safe debulking post-chemotherapy; mutilating surgery avoided.
• Survival exceeds 90%.

High-Risk Disease

• Encompasses >18 months Stage M, any MYCN amplified tumor, and toddlers (12-18 months) Stage M with unfavorable biology.
• Phase 1: Induction Therapy
  • Maximally reduce tumor burden.
  • Dose-intensive multiagent chemotherapy: Topotecan, Cyclophosphamide, Cisplatin, Etoposide, Doxorubicin, Vincristine.
  • Primary tumor surgical resection attempted post-induction.
• Phase 2: Consolidation Therapy
  • Myeloablative chemotherapy followed by autologous peripheral blood stem cell (PBSC) rescue.
  • Tandem (two sequential) autologous stem cell transplants yield superior event-free survival compared to single transplant.
  • External beam radiotherapy to primary tumor bed and residual metastatic sites.
• Phase 3: Postconsolidation Therapy
  • Targets minimal residual disease.
  • Isotretinoin (13-cis-retinoic acid): Differentiating agent.
  • Dinutuximab (ch14.18): Monoclonal antibody targeting GD2 disialoganglioside.
  • GM-CSF: Co-administered with Dinutuximab.
• Long-term survival approximately 50% despite intensive multimodal intervention.

Oncologic Emergencies In Neuroblastoma

• Spinal Cord Compression: Invading paraspinal tumors cause neurologic deficits. Managed emergently with Dexamethasone and rapid initiation of chemotherapy. Surgical laminectomy reserved for chemotherapy failure (high risk of subsequent kyphoscoliosis),.
• Opsoclonus-Myoclonus-Ataxia Syndrome (OMAS): Managed via immune modulation (Corticosteroids, Intravenous Immunoglobulin, Rituximab). Neurologic sequelae frequently persist despite tumor eradication.