MMP9 and head and neck carcinoma: One study has investigated the intracellular Stat3-MMP9 axis, with HN4, HN6, and Cal27 (head and neck carcinoma) cells and showed that treatment with rhIL-8-induced Stat3 phosphorylation and MMP9 expression, which were counteracted by an addition of Stat3 phosphorylation inhibitor (cryptotanshinone) [29].