CTH and neoplasm: While our finding that CTHkd slowed GBM invasion was linked to cysteine and not H2S based on rescue studies, it is possible that CTHkd lowering H2S could have caused some of the tumor growth we noticed in the setting of reduced invasion in vivo with CTHkd, a potential mechanism by which CTH could contribute to the “go or grow” hypothesis in which invasive GBM cells suppress proliferative programs and vice versa (61).