Background Signal transducer and activator of transcription 3 (STAT3) has been implicated as an oncogene in several neoplastic diseases. However, the biological effects of STAT3 have not been extensively studied in rectal carcinogenesis.

Aims To evaluate STAT3 activation in advanced rectal cancers and its association with clinicopathological variables and prognosis.

Methods Nuclear immunohistochemical expression of phosphorylated STAT3 (p-STAT3) was studied in 104 advanced rectal cancers (T3–T4). All patients were participating in the EORTC 22921 trial to assess whether preoperative chemoradiotherapy followed by postoperative chemotherapy improved overall and progression-free survival.

Results Nuclear p-STAT3 expression was detected in 37.5% of rectal cancer patients. No correlation was observed between p-STAT3 and any clinicopathological variables tested. However, patients with tumours positive for p-STAT3 had significantly improved overall survival.

Conclusion These results highlight an unexpected role for nuclear p-STAT3 expression in advanced rectal cancers and need further investigation to clarify this finding.