Since MMP13 is upregulated concomitantly with the onset of cancer cell dissemination in the MMTV-PyMT model [16], we determined the metastatic burden in the lungs from end-stage MMTV-PyMT;Mmp13+/+ and MMTV-PyMT;Mmp13−/− mice using a morphometric approach [29]. The gene discussed is MMP13; the disease is cancer.