[Ki-1 lymphoma]

ALCL is widely recognized with its broad morphologic and phenotypic spectrum causing controversy in the diagnosis of this peculiar neoplasm. It is now beyond doubt that a significant proportion(64 to 84%) of the cases diagnosed as ALCL is closely associated with the expression of chimeric NPM-ALK protein activated by the (2;5) (p23;q35) chromosomal translocation, which can be detected by anti-p80NPM/ALK or ALK1 antibodies. Recently, some investigators including us asserted that these p80NPM/ALK or ALK1-positive(p80/ALK+) ALCLs represent a distinct genetic entity with occurrence in young patients and a favorable prognosis, and should be differentiated from the p80/ALK- tumors with the relatively aggressive clinical course. The p80/ALK+ lymphomas also revealed the characteristic morphology such as horseshoe-like, kidney-like or doughnut-like nuclei and frequent expression of EMA and cytotoxic molecules. However, these features are shared, though to a lesser degree, by other p80/ALK-negative lymphoid neoplasms. Indeed, it is indicated that cytotoxic ALCL cases may be either p80/ALK positive or negative, suggesting that the cytotoxicity and expression of p80/ALK are independent phenomena among the cases of ALCL of T- and null-cell type. Thus, several areas of disagreement and controversy that surround the diagnosis and categorization of ALCL remain.