When tumors are sufficiently differentiated, distinguishing between low-grade AC and SCC with high accuracy can be achieved by assessing tumor morphological features (WHO criteria for SCC sub-classification include the degree of keratinization and/or the presence of intercellular bridges, and squamous pearl formation, while AC is characterized by glandular differentiation and/or mucin production), in combination with immunohistochemical staining for tumor sub-type markers [63,65,67–82]. This evidence concerns the gene MUC5AC and neoplasm.