Furthermore, knockdown or overexpression of HDC activated or inhibited the expressions of IL-6, p-STAT3, and S100A9, thus supporting the finding that HDC, as an upstream cancer suppressor gene, catalyzes the formation of histamine, inhibiting ovarian cancer cell proliferation, migration, and invasion via the IL-6/STAT3/S100A9 pathway. Here, S100A9 is linked to ovarian cancer.