CBS and breast cancer: In mammals, H2S is mainly synthesized from cysteine or its derivatives by the enzymes CBS and CTH.[6] Here, we first compared the mRNA levels of CBS and CTH using the TCGA‐BC database and found that the mRNA levels of CTH were significantly more abundant than those of CBS (P < 0.0001, Figure1A), suggesting that CTH might be the dominant H2S synthesizing enzyme in BC tissues.