Diagnostic Utility of Epithelial Membrane Antigen (EMA) and Calretinin (CAL) in Effusion Cytology

Well-Differentiated Papillary Mesothelioma with Omental Calcifications: A Case Report and Review of the Literature

BACKGROUND Omental calcifications of the peritoneum are typically small and asymptomatic. However, larger psammomatous bodies that cause symptoms such as abdominal pain and bloating are often associated with tumors such as primary serous papillary carcinoma, mesothelioma, or metastatic ovarian cancer. CASE REPORT We describe omental calcifications in a 68-year-old woman who had been asymptomatic for the last 10 years. The case details the histomorphologic features and immunohistochemical signature of a 4.0×3.5×1.0 cm mass consisting of mature adipose tissue that was surgically removed together with an 8.5×6.5×1.8 cm irregular intra-abdominal/mesenteric mass composed of yellow-red fatty tissue. Microscopic sections contained fat with variable clustered classic/psammomatous calcifications, some with a thin epithelioid periphery, in association with a very focal and subtle papillary surface epithelial/mesothelial proliferation. Tumor cell invasion was not observed during examination. Immunohistochemical staining showed that mesothelial cells in the mass were strongly positive for calretinin and focally positive for EMA, CK903, and vimentin. Strong nuclear positivity for PAX8 was also reported. Additional stains were added in response to this pattern, showing strong positivity for CK8, moderate positivity for BAP1, focal positivity for ER, minimal positivity for CD56, and negativity for CK5/6 and D2-40. Three possible explanations are suggested for the phenomenon observed in the pathology slides: reactive mesothelial hyperplasia, well-differentiated papillary mesothelioma, or serous papillary carcinoma of the peritoneum. CONCLUSIONS Findings suggest that these calcifications are a benign, reactive phenomenon, and that the abundance of psammoma bodies may be related to ongoing crops of papillary mesothelial hyperplasia or benign well-differentiated papillary mesothelioma.

Diagnostic Value of the EZH2 Immunomarker in Malignant Effusion Cytology

BACKGROUND

Differentiating reactive mesothelial cells from metastatic carcinoma in effusion cytology is a challenging task. The application of at least 4 monoclonal antibodies including 2 epithelial markers (Ber-EP4, MOC-31, CEA, or B72.3) and 2 mesothelial markers (calretinin, WT-1, CK5/6, or HBME-1) are often useful in this distinction; however, it is not readily available in many resource-limited developing countries. Aberrant immunoexpression of enhancer of zeste homolog 2 (EZH2), a transcriptional repressor involved in cancer progression, is observed widely in various malignancy. In this study, we evaluate the diagnostic value of EZH2 as a single reliable immunomarker for malignancy in effusion samples.

METHODS

A total of 108 pleural, peritoneal, and pericardial effusions/washings diagnosed as unequivocally reactive (n = 41) and metastatic carcinoma (n = 67) by cytomorphology over 18 months were reviewed. Among the metastatic carcinoma cases, 54 were adenocarcinoma and others were squamous cell carcinoma (n = 1), carcinosarcoma (n = 1), and carcinoma of undefined histological subtypes (n = 11). Cell block sections were immunostained by EZH2 (Cell Marque, USA). The percentages of EZH2-immunolabeled cells over the total cells of interest were calculated. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut-off score to define EZH2 immunopositivity.

RESULTS

A threshold of 8% EZH2-immunolabeled cells allows distinction between malignant and reactive mesothelial cells, with 95.5% sensitivity, 100% specificity, 100% positive predictive value, and 93.2% negative predictive value (p < 0.0001). The area under the curve was 0.988.

CONCLUSION

EZH2 is a promising diagnostic biomarker for malignancy in effusion cytology which is inexpensive yet trustworthy and could potentially be used routinely in countries under considerable economic constraints.