SLC4A4 and rectal cancer: Interestingly, the SLC4A4 gene (Supplementary Figure S3B), which is involved in bicarbonate secretion and intracellular pH regulation, was also co-upregulated with CTSE. However, the correlations among CTSE, RAB27B, and SLC4A4 expression, uncontrolled mucus secretion and expansion, and CCRT resistance in rectal cancer require further investigation.