To gain insight into the molecular characteristics of ATCs developed by [Pten, p53]thyr−/− mice, we performed genome-wide expression profiling using the Affymetrix platform on thyroids from 3-month old control, single, and double mutant mice, as well as on five follicular and five anaplastic carcinomas developed by Ptenthyr−/− and [Pten, p53]thyr−/− mice, respectively. This evidence concerns the gene PTEN and undifferentiated carcinoma.