SERPINB2 and breast cancer: We generated SerpinB2-deficient MMTV-PyMT (SB2−/−;PyMT) mice by crossing SB2−/− mice with PyMT mice to provide insights into the in vivo function of SerpinB2 in mammary tumor development and progression and found that SerpinB2 deficiency resulted in a delay in PyMT-induced mammary tumor initiation and progression.