The present invention provides for a transgenic animal model that constitutively expresses a protein encoded by the NPM-ALK gene in lymphoid tissue, and exhibits enhanced and accelerated development of a T cell lymphoproliferative disorder or B cell plasma cell tumor, together with the identification of cells transduced with the ALK tyrosine kinase gene or fusion proteins thereof, and methods for using this animal model and cells for screening compounds or treatments for antitumor activity. In preferred embodiments, the animal is a transgenic mouse that expresses a human NPM-ALK gene operably linked to human regulatory sequences, and the cells of the mouse have at least one copy of the NPM-ALK transgene, whereby the mouse constitutively expresses a protein encoded by the NPM-ALK transgene. The animals and cells of the invention are useful in the study of NPM-ALK-dependent lymphomagenesis and plasma cell tumors and in the development of treatments for these conditions.