However, in certain conditions, STAT3 may play the role of tumor inhibitor, suppressing the progression of various cancers, including lung adenocarcinoma, glioblastoma, prostate cancer, colorectal cancer, thyroid cancer, breast cancer, and esophageal squamous cell carcinoma.35 ROP16 has serine/threonine kinase loci in its protein sequence and can activate STAT3 by phosphorylation. Here, MARK2 is linked to esophageal squamous cell carcinoma.