SERPINB2 and breast cancer: To investigate the potential in vivo role of SerpinB2 in breast cancer development and progression, SerpinB2-deficient PyMT (SB2−/−;PyMT) mice were produced by crossing SB2−/− female mice with C57BL/6 strain background PyMT males, and the PyMT transgene and SerpinB2-deficient genotype in all female offspring were analyzed by PCR (Fig. 1A).