Neuroblastoma is the most common malignancy in children and the third most common overall malignancy, following leukaemia and CNS tumours. It is a catecholamine secreting cancer, affecting approximately 100 children each year in the UK. It is rarely diagnosed in children over the age of five.

The tumour specifically comprises of neural crest cells, which differentiate to form the sympathetic chain and the adrenal glands in the lumbar areas. It often starts in the abdomen and has a 50% risk of metastasising to bones, liver and skin, through haematological and lymphatic spread.

Little is known about the aetiology of neuroblastoma. Considering the rarity of the malignancy, direct causes are difficult to ascertain, and specific environmental exposures have not been implicated in the development of the disease.

1% of patients have a family history of neuroblastic tumours. Mutations of ALK and PHOX2B are recorded at an increasing rate. Cases of neuroblastoma which coincide with other congenital abnormalities of the neural crest cells have been associated with PHOX2B germline mutations. This is a homeobox gene regulating autonomic nervous system (ANS) development. Other genes which act as tumour suppressor genes proven to be involved are located on chromosome 1 and 11.

Certain medical conditions are related to aberrant neural crest development and increase the risk of developing neuroblastoma. These include:

• Turner's syndrome
• Hirschsprung's disease
• Congenital central hypoventilation syndrome
• Neurofibromatosis type 1

Neuroblastoma is derived from the ventrolateral neural crest cells in the neuroectoderm, which migrate from the neural tube during early embryogenesis.

• 30% arise within the adrenal medulla
• 60% arise from abdominal paraspinal ganglia
• Remainder originate rom the sympathetic ganglia in the chest, head / neck and pelvis

Cascading signalling gradients of BMP, Wnt, Notch and other ligands stimulate cellular specialisation. Inhibition of this maturation process increases the propensity to malignant transformation.

EMT and MET transitions within the neural crest

• EMT = epithelial to mesenchymal transition (the crux of neural crest maturation)
• Transcriptional factors (ZIC1, PAX3, TPAP2a, Notch and PRDM1A) initiate the crest development pathway after neural tube formation
• Expression of the SOXE family and ZEB2 drive mesenchymal transformation
• BMP, Wnt and FGF further stimulate differentiation
• SOX1, FOXD3, C-Myc and MYCN allow cells to proliferate and become resistant to cell death

While neuroblastoma arises from disrupted development of neural crest precursor cells, a single gene or epigenetic mutation has not yet been attributed to this tumour. However:

• The MYCN oncogene stimulates neuroblastoma tumorigenesis and predisposes patients to a particularly aggressive form of cancer
• ALK (anaplastic lymphoma kinase) is also implicated as an oncogene in neuroblastoma
• PHOX2B (a homeobox gene) is found in a small population of familial neuroblastoma and also in some sporadic cases

Pathological hallmarks of Neuroblastoma

• Homer-Wright rosettes: seen in 25-30% of cases. They consist of an arrangement of tumor cells around a central area of neurofibrillary processes.
• Small round blue cells with hyperchromatic nuclei
• Bombesin positivity: bombesin is a tumour marker for multiple malignancies such as neuroblastoma, small cell carcinoma of the lung, pancreatic cancer and gastric cancer.

The most common presenting symptom is due to the mass effect of the primary lesion (e.g., constipation, abdominal distention) or the result of metastases (e.g., bone pain). This may be accompanied with generalised symptoms such as fatigue, malaise, fever and failure to thrive. However, patients with localised disease may be asymptomatic.

Other signs and symptoms depend upon where the tumour is initially located and where it has metastasised. Close to 70% of children with neuroblastoma will have a metastasis:

• Spinal cord: numbness, weakness, loss of movement at the level of the spinal cord
• Neck: breathlessness, dysphagia, Horner's syndrome
• Bone (most common site of metastasis): pain and swelling
• Bone marrow
  • Thrombocytopenia causes bleeding and bruising
  • Anaemia causes fatigue, shortness of breath and pallor
  • Leukopenia increases the propensity to infections
• Skin: small, raised, blue/black discoloured lumps
• Liver: hepatomegaly and abdominal pain

NICE cancer referral guidelines for neuroblastoma suggest the following:

The 2015 NICE guidelines recommend a very urgent referral (within 48 hours) for specialist assessment of neuroblastoma if the patient presents with:

• Organomegaly and / or
• Visible and unexplained haematuria.

Symptoms may warrant a telephone discussion with a secondary care specialist if there is uncertainty and a questionable sense of urgency.

Request the following initial investigations:

• Urine catecholamines are a sensitive and specific marker for neuroblastoma: often high levels of the tumour markers vanillylmandelic acid (VMA) and homovanillic acid (HVA), the breakdown products of noradrenaline and adrenaline.
• Bloods
  • May reveal pancytopenia, in which case patients need blood or platelet transfusion prior to biopsy. This suggests metastasis
  • Serum electrolytes may reflect tumour lysis syndrome (should be treated prior to chemotherapy)
  • Serum creatinine / urea may be elevated if there is renal vasculature involvement. This influences the doses of contrast in radiological studies and chemotherapy
  • Serum catecholamine levels or their metabolites are usually high
  • LFTs may be elevated and should be corrected if abnormal on initial investigation. Abnormal LFTs warrant further investigations, secondary to metastasis
  • Serum LDH may be elevated.
• Imaging
  • Abdominal USS
  • If a mass is detected, further imaging should include a CT or MRI of the abdomen.
• Other tests include:
  • MIBG scan
  • Bone scan
  • Biopsy to determine type of tumour.

The most common differential diagnosis for Neuroblastoma is Wilms' tumour. Whilst both present with an unexplained abdominal mass, Wilms' tumour is often accompanied by haematuria and the presence of congenital overgrowth syndrome (e.g., Beckwith-Wiedemann syndrome, Perlman syndrome, Sotos syndrome).

• CT or MRI of the abdomen or pelvis shows claw sign (a renal mass with parenchyma stretching around the tumour)
• Wilms' tumour is bilateral in 5-10% of cases

A rhabdomyosarcoma may present similarly to a neuroblastoma; the most common primary site is the genitourinary system.

• Fluorescence in situ hybridisation (FISH) maps the genetic material in a cell; on biopsy sample this will show PAX3-FOXO1 or PAX7-FOXO1 gene rearrangement for the alveolar subtype

Also consider other causes of raised HVA and VMA in serum / urine:

• Pheochromocytoma:
  • Uncommon in children
  • Risk factors include multiple endocrine neoplasia syndrome type 2A and B, Von-Hippel-Lindau disease, neurofibromatosis type 1.
  • A tumour arising from chromaffin cells of the adrenal medulla.
  • Classically presents with headaches, diaphoresis, and palpitations in the setting of paroxysmal hypertension.
• Other neural crest tumours

In order to internationally standardise staging irrespective of surgery, the International Risk Group developed a staging system based on image-defined risk factors (IDRFs). The IDRFs are determined before surgery, at point of diagnosis.

Patients are divided into four groups:

• L1: localised tumour not involving vital structures, as defined by the list of IDRFs (below), and confined to one body compartment
• L2: local-regional tumour with presence of one or more IDRFs
• M: distant metastatic disease (except stage MS tumour)
• MS: metastatic disease in children younger than 18 months, with metastases confined to the skin, liver, and/or bone marrow.

IDRFs:

• Multiple body compartments: ipsilateral tumour extension within 2 body compartments (i.e., neck and chest, chest and abdomen, or abdomen and pelvis).
• Neck:
  • Tumour encasing carotid artery, vertebral artery, and/or internal jugular vein
  • Tumour extending to skull base
  • Tumour compressing trachea.
• Cervicothoracic junction:
  • Tumour encasing brachial plexus roots
  • Tumour encasing subclavian vessels, vertebral artery, and/or carotid artery
  • Tumour compressing trachea.
• Thorax:
  • Tumour encasing aorta and/or major branches
  • Tumour compressing trachea and/or principal bronchi
  • Lower mediastinal tumour infiltrating costovertebral junction between T9 and T12 vertebral levels.
• Thoracoabdominal junction: tumour encasing aorta and/or vena cava.
• Abdomen and pelvis:
  • Tumour infiltrating porta hepatis and/or hepatoduodenal ligament
  • Tumour encasing branches of superior mesenteric artery at mesenteric root
  • Tumour encasing origin of celiac axis and/or origin of superior mesenteric artery
  • Tumour invading 1 or both renal pedicles
  • Tumour encasing iliac vessels
  • Pelvic tumour crossing sciatic notch.
• Intraspinal tumour extension: (whatever the location) provided that more than one-third of the spinal canal in axial plane is invaded, the perimedullary leptomeningeal spaces are not visible, or the spinal cord signal intensity is abnormal.
• Infiltration of adjacent structures and organs: pericardium, diaphragm, kidney, liver, duodenopancreatic block, and mesentery.

The management approach depends on which risk category the patient falls under. Treatment may vary from observation to intense multimodal therapy. Patients should be under the care of a paediatric oncologist, cancer surgeon and radiation oncologist.

A biopsy is required to diagnose the tumour biology and chromosomal arrangements. It gives information regarding:

• Risk stratification
• Stage of disease
• Presence or absence of MYCN (v-myc avian myelocytomatosis viral oncogene neuroblastoma derived homolog) amplification
• Tumour cell polity
• Chromosomal abnormalities
• Histopathology of the tumour.

Age is significant for risk stratification; the younger the patient, the better the survival rate. The Children's Oncology Group (COG) places patients into three risk groups, which predict prognosis. The International Neuroblastoma Staging System (INSS) is used in this classification.

Low-risk disease:

• Any age with stage 1 (completely removed) disease
• Any stage 2 disease in patients <365 days of age
• Stage 2 disease in patients >365 days to 21 years of age with non-amplified MYCN
• Stage 2 disease in patients >365 days to 21 years of age with amplified MYCN and favourable histology
• Stage 4S disease with non-amplified MYCN, DNA index >1, and favourable histology.

Surgery is the first line treatment for patients who can safely have more than 50% of the tumour removed as determined by IDRFs. This may be followed by chemotherapy (carboplatin, etoposide, cyclophosphamide and doxorubicin).

Observation with serial ultrasounds every 3-6 weeks is a reasonable alternative for some patients depending on biopsy findings and staging. If tumour enlargement is noted during observation, surgery should be reconsidered.

Intermediate-risk disease:

• Stage 3 disease in patients <365 days of age with non-amplified MYCN
• Stage 3 disease in patients >365 days of age with non-amplified MYCN and favourable histology
• Stage 4 disease in patients <365 days of age with non-amplified MYCN
• Stage 4S disease, non-amplified MYCN, and either unfavourable histology or DNA index is 1.

Here the first line management strategy is chemotherapy (carboplatin, etoposide, cyclophosphamide and doxorubicin) usually for 4-8 cycles. Consult local guidelines for chemotherapy regimes.

Surgery is recommended for all patients in this group, with some patients requiring radiotherapy if chemotherapy and surgery are ineffective.

High-risk disease:

• Stage 3, 4, or 4S disease with amplified MYCN
• Stage 2 disease in patients >365 days of age with amplified MYCN and unfavourable histology
• Stage 3 disease in patients with non-amplified MYCN and unfavourable histology
• Stage 4 disease in patients >365 days of age.

High risk patients are started on induction chemotherapy comprising carboplatin, etoposide, cyclophosphamide and doxorubicin a chemotherapy regime for 5-6 cycles. Usually the drugs are given at higher doses compared to the low and intermediate risk groups. Again, consult local protocols for chemotherapy guidelines.

Surgery is recommended for all patients in this group once chemotherapy has decreased the initial tumour volume.

After induction chemotherapy and surgical removal, the next phase constitutes high dose chemotherapy followed by autologous bone marrow transplant. Myeloablative therapy has prevented event-free survival, but the impact on overall survival rate is still questionable.

• Conditioning chemotherapy regimes vary from trust to trust, but combinations include carboplatin, etoposide, cyclophosphamide, melphalan, busulfan, and thiotepa.
• There are questions regarding the optimum regime as the two most common combinations, busulfan plus melphalan (BuMel) and carboplatin plus etoposide plus melphalan (CEM), have different toxicity profiles. In clinical trials, BuMel improved event-free survival with reduced side effects compared to CEM, in high risk patients.

Radiation to the primary site is recommended in all patients.

Isotretinoin has become a maintenance therapy since it promotes differentiation of neuroblastoma cells into normal cells.

The INRG has produced four risk groups, which the COG system is likely to adopt in the future. Currently, trials are testing the impact of age <18 months, as well as chromosomal 1p or unbalanced 11q loss of heterozygosity on the risk stratification results. Different staging systems are preferred in different trusts.