Distribution of NPM1-ALK and X-ALK fusion transcripts in paediatric anaplastic large cell lymphoma: a molecular-histological correlation.

Anaplastic large cell lymphomas (ALCL) in children express anaplastic lymphoma kinase (ALK) fusion genes, most commonly NPM1-ALK. The distribution of X-ALK among 66 childhood ALCLs was analysed. One ALCL was ALK-negative. Reverse transcription polymerase chain reaction detected NPM1-ALK in 58 tumours, all showing nuclear and cytoplasmic ALK staining. The remaining seven ALCL stained for ALK in the cytoplasm only: two expressed TPM3-ALK, one ATIC-ALK, one MYH9-ALK; three no TPM3-, TFG-, ATIC-, CLTC- or MYH9-ALK. Almost 90% of paediatric ALK-positive ALCLs express NPM1-ALK. There was complete concordance between ALK staining pattern and the presence of a typical/variant ALK fusion partner.