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. Here, RAB27B is linked to rectal cancer.