ALK oncogene double-transgenic mice develop B-cell lymphoma. Comparison of immunohistochemical stainings of lymph nodes from tTA control littermate (A-C), TPM3-ALK (ON; D-F), and NPM-ALK (ON; G-I) double transgenic mice. Serial sections show a massive involvement by lymphoma cells of B phenotype positive for B220 (D,G) and Pax5 (E,H). Negative areas (*) correspond to residual T cells positive for CD3 (F,I; original magnification ×40).