Background: Endoscopic papillectomy of duodenal papillary tumors (PT) is indicated for adenomas or well-differentiated adenocarcinomas that do not involve the sphincter of Oddi. However, there is currently no reliable pre-operative method to diagnose the infiltration in the sphincter of Oddi.’ Insulin-like growth factor 2 mRNA protein 3 (IMP3) staining is reportedly associated with advanced disease stage and clinical outcomes in many carcinomas. The aim of this retrospective study was to investigate the ability of diagnosing sphincter of Oddi involvement in PT and predicting the prognoses using IMP3 immunohistochemistry. Methods: Twenty-five resected specimens from patients with PT and 24 biopsy specimens from the same patients excluding one were immunostained for IMP3. The percentage of positive cells in the tumor was evaluated and compared with the final pathological diagnosis and prognosis. Results: The final pathological diagnoses were adenoma in 5 patients and adenocarcinoma in 20 patients (no sphincter of Oddi involvement in 5 and involvement in 15). The ability to diagnose sphincter of Oddi involvement based on the percentage of IMP3-positive cells in resected specimens and tissue biopsies was the area under the curve 0.8 and 0.78, respectively, of the receiver operating characteristic curve, and the accuracies were 80.0% and 75.0% (cutoff value: 10%), respectively. Moreover, patients with an IMP3-positive cell rate of ≥ 10% had a significantly worse prognosis (log-rank test P = 0.01). Conclusion: IMP3 immunostaining of resected and biopsy specimens from PT patients enables the diagnosis of sphincter of Oddi involvement objectively and is also effective in predicting the prognosis.
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