RET and neoplasm: However, we found that thyroid tumors from 4-month-old and 8-month-old RET/PTC3 Dicer1(−/−) mice were significantly smaller than those from RET/PTC3 Dicer1(+/−) and RET/PTC3 Dicer1(+/+) mice, indicating that the complete loss of Dicer1 leads to a reduction in tumor size.