Using the a gompertzian growth function (see equation (1) in the Methods section) and the observed mean values for the tumor weight and the duration of the experiment (1.23 g and 49.9 days for pfp/rag2; 1.16 g and 69.4 days for rag2 mice) a growth rate constant of 0.0462 day-1 was determined for pfp/rag2 mice and 0.0326 day-1 for rag2 mice. The gene discussed is PRF1; the disease is neoplasm.