TTF1 and neoplasm: 4.Primitive alveolar epithelial cellorigin3, 4, 5, 6:Through the immunohistochemical study of 100 SHL cases, Devouassoux et al.3 found that TTF-1, SPB, EMA and CK positive expression rates in tumor cells were very high, and that TTF-1 and SPB were the characteristic antigens of alveolar epithelial cells.