Some key tumor immunohistochemical markers (e.g., positive calretinin, CK7, and WT-1, with negative CEA) and cellular characteristics (epithelioid, poorly differentiated) are commonly seen for both mesothelioma and PSC (Fox, 1993; Schorge et al., 2000; Shimizu et al., 2000; Al-Hussaini et al., 2004; McCoubrey et al., 2005; Kobel et al., 2008). The gene discussed is CALB2; the disease is mesothelioma.