Mesothelioma in Situ With a TP53 Mutation

We report a case of mesothelioma in situ giving rise to invasive mesothelioma and associated with a long in-frame TP53 deletion. Tumor arose in the peritoneal cavity in a 55-year-old man. BAP1, MTAP, and NF2/merlin were retained by immunohistochemistry, but p53 was overexpressed by immunohistochemistry in the flat mesothelioma in situ, papillary mesothelioma in situ, and invasive mesothelioma. Almost all cases of mesothelioma in situ that have been previously described have a BAP1 mutation/deletion; this is the first example of mesothelioma in situ associated with a TP53 mutation, and suggests that staining for p53 may be useful in evaluating potential mesothelioma in situ cases.