These two mouse models were deemed necessary primarily for three reasons, i.e. to examine the MB loss-of-function (LoF) (i) in the context of p53-deficient (WapCre;Trp53flox/MB) vs. p53-wildtype or p53-mutant tumor backgrounds (PyMT/MB) for an assessment of MB’s alleged tumor suppressor role in relation to p53 status; (ii) in the context of both genesis (grade, type) (WapCre;Trp53flox/MB) and progression (i.e. tumor cell dissemination and metastasis formation (PyMT/MB)) of primary malignancies; and (iii) in the context of mammary tumorigenesis with different tumor onset and tumor load. Here, TP53 is linked to neoplasm.