β‑catenin expression in endometrioid type endometrial cancer: Expression patterns and impact on disease outcomes

Determination of nuclear and/or cytoplasmic expression of β-catenin by immunohistochemistry in patients with endometrial cancer (EC) may constitute a potential diagnostic method for identifying patients with a catenin β1 (CTNNB1) gene mutation and those at risk of disease recurrence. The present study aimed to investigate β-catenin expression patterns in hysterectomy specimens of patients with endometrioid type EC using immunohistochemistry, and to examine the prognostic impact of β-catenin. The study was a single-institutional, retrospective cohort trial enrolling consecutive patients with a postoperative histopathological diagnosis of endometrioid EC who underwent hysterectomy between January 2015 and December 2018. Histopathology slides from 75 patients were stained with a monoclonal antibody targeting the β-catenin protein. Any percentage of nuclear staining, whether focal or diffuse, was considered 'β-catenin nuclear-positive'. The cytoplasmic staining reaction of β-catenin was assessed based on the percentage of stained cells and staining intensity. Immune-reactivity score (IRS) values were determined by multiplying the scores for the percentage of staining and staining intensity. IRS values 0 to 2 were regarded as negative expression, 3 to 4 as low expression, 6 to 8 as moderate expression, and 9 to 12 as high expression. Recurrence-free survival (RFS) was used as the prognostic endpoint. Only 2 out of 75 tissue samples (2.7%) exhibited nuclear β-catenin expression, with a low staining percentage of 5%. By contrast, cytoplasmic staining was observed in all samples (100%). According to the IRS findings, 1.3% of the samples exhibited negative cytoplasmic expression, 42.7% low expression, 38.7% moderate expression and 17.3% high expression. Cox regression analysis revealed that staining with β-catenin, either nuclear or cytoplasmic, had no impact on RFS, and stage was the sole independent prognostic factor. In conclusion, based on these results, β-catenin expression in endometrioid EC was revealed to be mostly cytoplasmic, with only 2.7% of tissue samples exhibiting nuclear expression. Overall, β-catenin expression has no impact on RFS.