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Abstract

Ewing Sarcoma (ES) is a small round cell tumour of neurectodermal origin commonly seen in the pediatric age group. Uncommon sites of occurence of Ewing sarcoma poses a diagnostic and therapeutic challenge. We report a rare case of extraosseous Ewing Sarcoma (EOES) arising from the parotid gland in a child. This case report compares the clinical characteristics and outcome of all the cases of paediatric parotid gland EOES described in literature. 1. Introduction

Ewing Sarcoma (ES) is a common malignant neurectodermal tumour of childhood with osseous (arising from the bone) or extraosseous (arising from soft tissue without involvement of bone) origin. Extraosseous Ewing Sarcoma (EOES) is uncommon [1] and a fifth of all tumours occur in the head and neck region. However, tumour arising from salivary glands is rare [2]. We report an unusual case of a child with parotid gland EOES.

2. Case report

A nine-year-old boy presented with complaints of a progressively enlarging swelling in the right parotid region associated with difficulty in mouth opening since 2 months. There was no history of pain, fever or discharge from the site. Physical examination revealed a solitary oval swelling measuring 8 × 6 cm in the right parotid region. It was non tender, firm in consistency, immobile and non pulsatile. Prominent veins were present over the swelling (Fig. 1). Mouth opening was restricted but not painful. On intraoral examination, the opening of the parotid duct was normal. A diagnosis of EOES can be established by imaging, morphologic and immunohistochemistry studies. ES is a small blue round cell tumour which expresses CD99/MIC2 in approximately 97% of EWS/PNET [18]. However, it is also positive in acute lymphoblastic lymphoma/leukemia and rhabdomyosarcoma which are the other differential diagnoses in this case. Immunoreactivity with CD99 in addition to vimentin and BCL-2 and absence of LCA, desmin, myogenin, synaptophysin, cytokeratin etc rules out lymphoma, rhabdomyosarcoma, carcinoma and neuroblastoma establishing a diagnosis of EOES in this case.

The most common translocation, t(9; 11)(p22; q23), may be detected by traditional karyotype, FISH or Polymerase chain reaction analysis. However, alternate translocations with other chromosomes bearing members of the ETS family would not be detected by the FISH test used and is likely to be the cause of a negative test result in the index case [14]. Work-up for alternate translocations was not performed in the present case due to financial limitations.

Multimodality treatment approach including multiagent chemotherapy, radiation therapy and surgery can lead to 5-year overall survival of 65% in localised ES [19]. Tumor-free margins irrespective of the quantitative extent of negative margins is sufficient to achieve optimal local control of EOES [20]. Radiation therapy in ES is indicated for incomplete surgical resection or inadequate histological response to improve rates of local control [19].

4. Conclusion

Extraosseous Ewing Sarcoma of the parotid gland is a rare entity, and can pose a diagnostic and therapeutic challenge. Nevertheless with multimodality therapy including surgery, chemotherapy and radiotherapy, a long-term cure can be achieved, as we demonstrated in our patient