These results indicate a cooperative role of Patz1-null mutation with RET/PTC1 in enhancing thyroid cancer cell proliferation, accounting for the higher aggressive phenotype of tumors developed by RET/PTC1TG mice, heterozygous or homozygous for the Patz1-knockout mutation, compared to single mutant RET/PTC1TG mice. The gene discussed is RET; the disease is thyroid gland carcinoma.