Sixty-two cases showed the immunohistochemical staining patterns similar to their parental LUSC tumors, as determined by IHC with antibodies against human squamous cell carcinoma-specific proteins, CK5, p63, and TTF1 (three typical cases shown in Fig. 1b); whereas, 16 cases were found to have xenograft-associated lymphoproliferative diseases (XALDs), and 4 cases showed histologically different stromal patterns, compared to the parental patient tumors, which were even distinctive from most of the other PDX tumors for unknown reasons. This evidence concerns the gene TTF1 and squamous cell carcinoma.