PTPN6 and esophageal squamous cell carcinoma: Reports suggest the transcriptional repression of the PTNP6 promoter by hypermethylated CpG islands during the regulation of SHP-1 expression, which shows tumor suppressor activity in hematological malignancies [17,18,19], esophageal squamous cell carcinoma [20], and gastric adenocarcinoma [21,22].