The chromosomal translocation t(2;5)(p23;q35) is associated with "Anaplastic large cell lymphomas" (ALCL), a Non Hodgkin Lymphoma occurring in childhood. The fusion of the tyrosine kinase gene-ALK (anaplastic lymphoma kinase) on chromosome 2p23 to the NPM (nucleophosmin/B23) gene on chromosome 5q35 results in a 80 kDa chimeric protein, which activates the "survival" kinase PI3K. However, the binding mechanism between truncated ALK and PI3K is poorly understood. Therefore, we attempted to elucidate the molecular interaction between ALK and the regulatory p85 subunit of PI3K. Here we provide evidence that the truncated ALK homodimer binds to the SH3 domain of p85. This finding may be useful for the development of a new target-specific intervention.