BRCA1 and breast neoplasm: Somatic abrogation of BRCA1 and TP53 in conditional mouse models usually gives rise to high-grade breast tumors; nonetheless, some mice may develop well-differentiated tumors.112 Taken together, these findings support the contention that the concurrent loss of function of BRCA1 and TP53 does not necessarily result in the development of high-grade breast cancers.