Phosphorylation of hTERT at threonine 249 is a novel tumor biomarker of aggressive cancer with poor prognosis in multiple organs

Recent evidence indicates that RNA‐dependent RNA polymerase (RdRP) activity of human telomerase reverse transcriptase (hTERT) regulates expression of target genes and is directly involved in tumor formation in a telomere‐independent manner. Non‐canonical function of hTERT has been considered as a therapeutic target for cancer therapy. We have previously shown that hTERT phosphorylation at threonine 249 (p‐hTERT), which promotes RdRP activity, is an indicator of an aggressive phenotype and poor prognosis in liver and pancreatic cancers, using two cohorts with small sample sizes with polyclonal p‐hTERT antibody. To clarify the clinical relevance of p‐hTERT, we developed a specific monoclonal antibody and determined the diagnostic and prognostic value of p‐hTERT in cancer specimens using a large cohort. A monoclonal antibody for phosphorylated hTERT (p‐hTERT) at threonine 249 was developed and validated. The antibody was used for the immunohistochemical staining of formalin‐fixed, paraffin‐embedded specimens from 1523 cases of lung, colon, stomach, pancreatic, liver, breast, and kidney cancers. We detected elevated p‐hTERT expression levels in cases with a high mitotic activity, high pathological grade, and high nuclear pleomorphism. Elevated p‐hTERT expression was an independent prognostic factor for lung, pancreatic, and liver cancers. Furthermore, p‐hTERT expression was associated with immature and aggressive features, such as adenosquamous carcinoma (lung and pancreas), invasive type of cancer (lung), high serum alpha‐fetoprotein level (liver), and triple‐negative status (breast). In conclusion, RdRP activity indicated by p‐hTERT expression predicts aggressive cancer phenotypes in various types of cancer. Thus, p‐hTERT is a novel biomarker for the diagnosis of aggressive cancers with a poor prognosis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.