BRCA1 and breast cancer: Pathological analysis revealed that p18mt;Gata3+/- mammary tumors were highly heterogeneous and with various degrees of whorls and clusters of spindle-shaped cells, which are typical morphological characteristics of mesenchymal cells and also frequently observed in p18mt;Brca1+/-mammary tumors (Figure 4C, 5A, and Ref 7).