TGFB1 and papilloma: In contrast to the suppressive effects of TGFβ1 overexpression on papilloma formation [45, 90], continuously elevated levels of TGFβ1 appear to promote formation of highly undifferentiated spindle carcinoma [90], and 15 weeks of TGFβ1 overexpression in benign papillomas lead to increased invasiveness and metastases [45].