MUC5AC and cancer: Recently, we have found that as cancer advances to malignant stage, loss of giantin functions as a major Golgi matrix protein involved in the maintenance of Golgi morphology [20] and the primary Golgi targeting site for endoplasmic reticulum (ER)‐derived vesicles [21, 22, 23, 24, 25] results in fragmentation of the Golgi complexes [22, 25] as well as alteration of both N‐glycans [23, 24, 26, 27, 28] and mucin O‐glycans [22, 29, 30, 31, 32, 33, 34].