The clinicopathologic features of anaplastic large cell lymphoma (ALCL) are
reviewed. ALCL is a heterogeneous group of tumours, and histologic examina
tion alone is not adequate in providing useful prognostic information. Howe
ver, using a combination of clinical, phenotypic, and genotypic features, s
everal distinct clinicopathologic entities have been identified. A subset o
f ALCL as presently defined is characterized by a balanced translocation, t
(2;5)(p23;q35), resulting in a novel fusion protein (NPM-ALK) that can be r
eadily detected by immunohistochemical methods using antibodies against the
ALK protein. Detection of ALK protein, along with other methods for demons
trating the t(2;5), has assisted in identifying a distinct biologic entity
within the heterogeneous group of ALCL with significant prognostic implicat
ions. It is important to separate these from cases of ALK-negative ALCL, wh
ich have a poorer prognosis, and cases of primary cutaneous ALCL, which hav
e an excellent prognosis. Copyright (C) 1999 John Wiley & Sons, Ltd.