Eleven of 24 (45.8%) patients with high-grade appendiceal malignancies (8 with acellular mucin, 2 with adenocarcinoma), 2 of 18 (11.1%) with colorectal cancer (both with acellular mucin), 2 of 3 (66.7%) with mesothelioma, and 1 of 3 (33.3%) with ovarian carcinoma (with adenocarcinoma) had OHOM. The gene discussed is MUC5AC; the disease is mesothelioma.