Overexpression of cystathionine-β-synthase (CBS) in tumor cells leads to an increase in H2S levels (0.3 to 3.4 mM), especially in colon tumor cells.45 So, it will be more efficient to use H2S-activated therapy for colon cancer than other tumor microenvironment factors (pH, GSH, etc). This evidence concerns the gene CBS and colonic neoplasm.