In this study, we have uncovered that niraparib could upregulate the expression of GTP cyclohydrolase 1 (GCH1), a vital rate-limiting enzyme for the cofactor of nitric oxide synthases (NOSs) tetrahydrobiopterin (BH4) synthesis and an important participant in many chronic diseases, even malignant tumors, through JAK-STAT signaling [21–24]. This evidence concerns the gene GCH1 and cancer.