Tang D, et al. - By analyzing data on 268 eligible postoperative patients who received a diagnosis of gastrointestinal stromal tumor (GIST), researchers assessed the prognostic significance of proenkephalin (PENK) in GISTs. In GIST tissues categorized using the United States National Institutes of Health (NIH) risk classification system, they determined PENK expression. Findings revealed the association of PENK expression with tumor size, mitosis count per 50 high-power fields, and tumor rupture. Superior overall survival (OS) and recurrence-free survival (RFS) were reported in relation to high PENK expression, while worse OS and RFS were reported in relation to low PENK expression, in Kaplan–Meier analysis. In the entire population, OS and RFS were independently predicted by PENK. A close relation of PENK expression in GIST with NIH risk grade and prognosis was observed, which is suggestive of the possible role of PENK as a tumor suppressor and as a novel biomarker for predicting prognosis in postoperative GIST patients.