Use of E-cadherin and CD44 aids in the differentiation between reactive mesothelial cells and carcinoma cells in pelvic washings.

BACKGROUND

The presence of malignant cells in peritoneal washings is an independent prognostic factor in the evaluation of gynecologic malignancies. The differentiation between reactive mesothelial cells and carcinoma cells can be a diagnostic challenge based on morphology alone. The expression of some cell adhesion molecules may be helpful in the differential diagnosis.

METHODS

To evaluate the specificity of 2 transmembrane cell adhesion proteins (E-cadherin and CD44) in the differentiation of mesothelial cells from carcinoma cells in pelvic washings, formalin fixed, paraffin embedded cell blocks of pelvic washings from 19 cases of metastatic ovarian adenocarcinoma and 16 cases of benign peritoneal washings were immunostained with monoclonal antibodies to E-cadherin and CD44. The staining patterns were evaluated blindly by three observers. Positive staining was defined as uniform membranous staining for each marker.

RESULTS

Fourteen benign peritoneal washings (87.5%) demonstrated immunoreactivity with anti-CD44. On the contrary, only four adenocarcinomas (21.1%) demonstrated anti-CD44 immunoreactivity. E-cadherin expression was identified in only 2 benign peritoneal washings (12.5%) whereas 16 adenocarcinomas (84.2%) strongly expressed E-cadherin. The differences in immunostaining for both CD44 and E-cadherin between benign and malignant peritoneal washings were statistically significant. The combination of positive staining for E-cadherin and negative staining for CD44 was 100% specific for metastatic adenocarcinoma, whereas a combination of negative staining for E-cadherin and positive staining for CD44 was 100% specific for reactive mesothelial cells.

CONCLUSIONS

Both E-cadherin and CD44 reliably distinguish reactive mesothelial cells from adenocarcinoma. The combination of E-cadherin/CD44 is highly specific and is a useful diagnostic adjunct with which to distinguish benign reactive mesothelial cells from adenocarcinoma in pelvic washings.