TGFA and neoplasm: We found that Tgf-α mutant tumors had elevated numbers of TUNEL-positive apoptotic cells compared with Tgf-α competent tumors (see representative panels—Fig. 4 H-I), whereas there were no changes in proliferation rate or tumor vascularity, indicating that Tgf-α functioned to enhance tumor growth by limiting the rate of cancer cell apoptosis.