MUC5AC and mucinous neoplasm: While by definition, acellular mucin itself is benign, it may indicate the presence of nearby neoplastic mucin-producing cells, which can be missed on pathologic evaluation if infrequently distributed in the specimen, and some patients with resected peritoneal acellular mucin for low-grade appendiceal mucinous neoplasms have been known to recur.8,19,20 If the acellular mucin cases are excluded from the OHOM group in our study, we still identified approximately 10% of grossly normal omentums with histological omental metastases.