[4] The major constituents of mucus, the viscous secretion that covers epithelial surfaces such as those in the trachea, colon, and cervix, are highly glycosylated proteins called mucins.

This gene encodes an integral membrane glycoprotein found on the cell surface, although secreted isoforms may exist.

[5] MUC-4 has been found to play various roles in the progression of cancer, particularly due to its signaling and anti-adhesive properties which contribute to tumor development and metastasis.

[7] This beta subunit is considered an oncogene, whose role in cancer is increasingly being recognized particularly due to its involvement in signalling pathways, particularly with ErbB2 (Her2).

[10] Over 24 splice variants have been found for MUC4 using commercial mRNAs or total RNAs extracted from cancer cell lines.

[8] MUC-4 is thought to play a role in cancer progression by repressing apoptosis and consequently increasing tumor cell proliferation.

Bile acids have been found to stimulate carcinogenesis in pancreatic ductal adenocarcinoma cells through increased expression of MUC4.

[22] Unlike pancreatic and esophageal cancers, MUC4 expression is suppressed in the primary tumor when compared to normal cells.

The initial reduction in MUC-4 appears to promote the transition to the primary tumor, but its subsequent increase in expression facilitate metastasis and ultimately increased malignancy[23] MUC4 is found to be overexpressed in papillary thyroid carcinoma, and could serve as a potential marker of malignancy and prognosis.

Polymorphisms in the MUC4 gene have been found to play a role in the progression of endometriosis and related infertility,[15] as well as dysplastic cervical disorders.