For example, β-lapachone (β-lap) is a soluble ortho-naphthoquinone with potent anti-tumor and radiosensitizing activity only in the presence of high NQO1 activity [108,109,110,111,112,113,114], which is only noted in most malignant tumors but not in normal tissues [109]. The gene discussed is NQO1; the disease is cancer.