Table 6.

Anaplastic large-cell lymphoma and Its differential diagnosis, summary from the Workshop

ALK expression correlates with young age, systemic disease, a cytotoxic epithelial membrane antigen- positive phenotype and usually a good prognosis, but there are important exceptions to this rule

A significant number of anaplastic large-cell lymphoma cases (40–65%) have extranodal disease either at a primary site or as part of a systemic process. The determination of the origin of extranodal anaplastic large-cell lymphoma (primary versus a systemic process) is critically important, particularly in the skin

ALK expression alone is not diagnostic of anaplastic large- cell lymphoma as ALK can be present in other tumours, principally inflammatory myofibroblastic and other soft tissue tumours, tumours of neural origin (neuroblastoma, glioblastoma), and a very rare ALK+ B-cell lymphoma

To make a diagnosis of ALK-negative anaplastic large-cell lymph oma there must be strict adherence to characteristic cytology (a large cell predominant population with abundant cytoplasm and pleomorphic, embryo or hallmark nuclei or wreath-like giant cells) and strong CD30 expression with a membrane and Golgi distribution in virtually every cell. In lymph nodes, some involvement of sinuses should be seen