Page 601 - Concise Pathology for Exam Preparation ( PDFDrive )

586 SECTION II Diseases of Organ Systems

• There is a uniform distribution of giant cells in GCT bone, unlike other giant cell lesions
wherein giant cells are focally aggregated.

Q. Describe the clinicopathological features of tumours of
neuroectodermal origin.

Ans. Tumours of neuroectodermal origin include the Ewing sarcoma family of tumours
(EFST) which further includes Ewing sarcoma (ES) and primitive neuroectodermal
tumour (PNET). PNET generally demonstrates a greater neuroectodermal differentiation
as compared to ES.

Clinical Features

• ES affects children and young adults (peak incidence between 5 and 20 years; rare after
30 years). PNET is seen in relatively older individuals.
• Both present as a lytic lesion in long bones; most common skeletal sites include femur,
tibia, humerus, pelvis and ribs (A skin tumour of the chest).
• In the long bones these arise from the medullary canal and are located in the diaphysis
or metaphysis.
• Pain, tenderness, swelling accompanied by fever, leucocytosis and elevated ESR are the
main presenting features (clinical presentation of EFST mimics chronic osteomyelitis).
Rarely, ES may present as a soft-tissue neoplasm without involvement of underlying
bone (extraskeletal Ewing sarcoma).

X-Ray

Reactive periosteal bone is laid in layers parallel to cortex (‘onion-skin’ appearance).

Microscopy (Fig. 21.16)
• Biopsy shows a highly cellular, infiltrative neoplasm consisting of sheets of tightly
packed, round cells with very scant cytoplasm separated into irregular nests/lobules by
fibrovascular septae (‘round blue cell tumour’).
• The tumour cells appear to be of two distinct types: the larger round cells with a high
nuclear/ cytoplasmic ratio, fine chromatin pattern and occasional small, inconspicuous
nucleoli and the smaller and darker cells with eosinophilic cytoplasm and hyperchro-
matic, ‘shrunken’ nuclei. The latter are actually degenerated cells, a finding typical of
Ewing sarcoma.
• The cells have ill-defined cytoplasmic borders with small amounts of vacuolated-to-clear
cytoplasm attributed to the presence of cytoplasmic glycogen that gives a granular posi-
tivity with PAS stain.
• Necrosis is prominent but tumour giant cells are rare. At places, tumour cells form
pseudorosettes (Homer–Wright rosettes).

Cytogenetics
Ninety-five percent cases show reciprocal translocation 11:22 (q24:q12). This transloca-
tion is common to ES and PNET.

Prognosis
• Haematogenous metastasis to lungs, liver, bones and brain leads to an early spread.
• Disease stage at diagnosis (including tumour volume) is the main prognostic factor for
patients with ES/PNET; use of combined chemotherapy and radiotherapy improves
clinical outcome.

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