TP53 and squamous carcinoma in situ: Scattered tumor cells illustrated weak or moderate positivity for p53 with rates ranging from 1 to 60% (Fig. 5d), which meant wild type pattern of TP53. Three cases of composite tumors showed negative staining both in small cell carcinoma and in adenocarcinoma or squamous cell carcinoma in situ, which suggested TP53 nonsense mutation.