To determine the impact of MMP11 on tumor necrosis and apoptosis in MMTV-PyMT mice, we analyzed paraffin-embedded #4 mammary gland tissue sections from PyMTTg; MMP11Tg and PyMTTg; MMP11KO mice and their control littermates by hematoxylin and eosin (HE) staining and Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assay. The gene discussed is MMP11; the disease is neoplasm.