Mucins are
glycoproteins synthesized by epithelial cells and thought to promote
tumor-cell invasion. Eight human
mucin genes have been well characterized: MUC2, MUC5AC, MUC5B, MUC6 map to 11p15.5 and encode secretory gel forming
mucins while MUC1, MUC3, MUC4, MUC7 are scattered on different chromosomes and encode membrane-bound or secreted
mucins. The expression pattern of the
mucin genes is complex in normal airways involving six genes, mainly MUC5AC and MUC5B in mucus-producing cells and MUC4 in a wide array of epithelial cells. MUC5AC overexpression in
metaplasia, dysplasia and normal epithelium adjacent to
squamous cell carcinoma provides additional arguments for a mucous cell origin of preneoplastic squamous lesions. MUC5AC and MUC5B expression is related to mucus formation in
adenocarcinomas. Mucinous
bronchioloalveolar carcinoma (BAC) has a particular pattern of
mucin gene expression indicating that it has sustained a well-differentiated phenotype similar to the goblet cell, correlated with distinctive features i.e. a noninvasive pattern and a better prognosis than nonBACs. MUC4 is the earlier
mucin gene expressed in the foregut, before epithelial differentiation and is expressed independently of mucus secretion both in normal adult airways and
carcinomas. These findings are in favor the histogenetic theory of non-
small-cell carcinoma originating from a pluripotent mucous cell.