Institute of Pathology, Department of Health, Sai Ying Pun Polyclinics

Small round cell tumours constitute a diverse group of neoplasms that are primitive or embryonal in appearance. They often lack specific morphologic features that would allow precise histologic identification. An awareness of the diverse lesions that may present as small round cell tumours is critical to arrive at the correct diagnosis. Immunohistochemical techniques and ultrastructural studies are indispensable in the diagnosis of these tumours and recent developments in cytogenetic and molecular genetic techniques have greatly facilitate the precise subtyping, classifications and determination of new tumoural entities that would provide guidelines for prognosis and therapy. This presentation describes the changing approach to the differential diagnosis of small round cell tumours with combined use of immunophenotypic, electron microscopic and genetic analysis.