MUC5AC and cancer: Both MUC1 and MUC4 are membrane-associated mucins involved in cellular contact and signalling and may play a role in the autonomous and dysregulated proliferation seen in cancer cells.47 These mucin proteins are not necessarily expressed simultaneously,21 and the combined evaluation of MUC1 and MUC4 expression might therefore increase sensitivity in detection of prognostically poor tumours among these patients.