SMAD3 and neoplasm: Although most Smad3−/− mice survived to endpoint, disease signs consistent with tumor development (diarrhea, hunched posture, blood in feces, weight loss, palpable mass in abdomen) necessitated euthanasia of 5/17 Smad3−/− mice (between 19.4 to 25.6 weeks) prior to the study endpoint of 27 weeks (Figure 1C).