Tumor progression was assessed by biweekly palpation from day 21 to day 98 and tumors were categorized according to their size (0, <0.5, 0.5 to 1, >1 cm) as presented in Figure 1C. At 10 weeks of age, MMTV-PyMT; Mmp8-wild-type (n = 26) and heterozygote (n = 34) mice showed similar tumor size distribution patterns with the majority of tumors being between 0.5 to 1 cm. This evidence concerns the gene MMP8 and neoplasm.