TCF7 and neoplasm: Analysis of components of the Wnt pathway confirmed that Tcf1 (Tcf7) expression was absent (as expected) in the Tcf1−/− thymocytes (with and without a tumor), whilst in all but one Tcf1−/− tumor sample, the expression level of the transcription factor Lef1 was up-regulated compared to control (Tcf1+/−) thymocytes (Figure 3A, left panel).