DICER1 and undifferentiated pleomorphic sarcoma: Furthermore, it has been reported that Dicer1 haploinsufficiency promotes the development of distant metastases in a preclinical mouse model of undifferentiated pleomorphic sarcoma (UPS) expressing Kras-G12D but not those expressing Braf-V600E23, suggesting additional complexity in the way distinctive alterations within the RAS/ERK pathways cooperate with DICER1 mutations.