MUC5AC and breast cancer: It has been previously found that in breast cancer, alterations in mucin expression or glycosylation influence tumor growth, adhesion, invasion, and immune surveillance.16,17 The impact of missense mutations resulting in an amino acid change to a serine residue on the glycosylation status of mucins is unknown, but it is tempting to speculate that these alterations could influence their function, stability and secretion.