The pathogenesis of large cell transformation in cutaneous T-cell lymphoma is not associated with t(2;5)(p23;q35) chromosomal translocation.

In 20%-50% of the advanced cutaneous T-cell lymphomas (CTCL), malignant T cells undergo large cell transformation (LCT). The malignant T cells of LCT in CTCL can share morphologic and immunophenotypic similarities with CD30 (Ki-1)-positive anaplastic lar-ge cell lymphoma (ALCL), suggesting a common mechanism of pathogenesis. The t(2;5) (p23;q35) translocation, resulting in the fusion of the nucleophosmin (NPM) gene and the anaplastic lymphoma kinase (ALK) gene, is associated with primary CD30+ ALCL. To determine whether acquisition of this chromosomal translocation is involved in the pathogeneis of LCT in CTCL, we examined 12 tumor samples from 9 CTCL patients, including 8 with LCT-CTCL and one with concurrent CTCL and Hodgkin's disease, for the presence of the t(2;5) translocation. Numerous CD30+ large cells were present in 4 LCT-CTCL consistent with secondary CD30+ ALCL; CD30 was expressed by <10% of the large cells in another case and was negative in the other 3 lymphomas. Using primers spanning the NPM/ALK fusion junction, PCR amplification following reverse transcription (RT) of mRNA failed to show the products of NPM/ALK fusion in all samples tested. Thus, the t(2;5) (p23;q35) translocation does not appear to be involved in the molecular pathogenesis of LCT in CTCL, including CD30+ cases. (C) Munksgaard 1997.