Wilms tumor 1/cytokeratin dual-color immunostaining reveals distinctive staining patterns in metastatic melanoma, metastatic carcinoma, and mesothelial cells in pleural fluids: an effective first-line test for the workup of malignant effusions.

BACKGROUND

The workup of a malignant effusion usually requires immunostaining with a panel of markers. Although nuclear Wilms tumor 1 (WT1) expression is widely used to detect tumors of ovarian and mesothelial origin, it is less well known that WT1 is also expressed in the cytoplasm of melanomas and mesenchymal tumors. Because to the authors' knowledge the diagnostic utility of cytoplasmic WT1 expression has not been explored to date, the usefulness of a WT1/AE1/AE3 dual-color immunostain in the workup of malignant effusions was evaluated.

METHODS

A total of 86 pleural effusions, including 17 metastatic melanomas, 31 metastatic adenocarcinomas, 10 malignant mesotheliomas, 10 lymphoproliferative disorders, 5 metastatic sarcomas, and 13 benign specimens, were immunostained using a peroxidase-based brown chromogen for WT1 and an alkaline phosphatase-based red chromogen for AE1/AE3 on cell block sections.

RESULTS

The majority of malignant effusions stained in 1 of 4 distinctive patterns: 1) all lung and breast adenocarcinomas demonstrated cytoplasmic AE1/AE3 expression without nuclear or cytoplasmic WT1 expression; 2) serous carcinomas of Müllerian origin, mesotheliomas, and benign mesothelial cells were positive for cytoplasmic AE1/AE3 as well as nuclear WT1; 3) melanomas, sarcomas, and a subset of plasma cell neoplasms were positive for cytoplasmic expression of WT1 but negative for AE1/AE3; and 4) large B-cell lymphomas and a subset of plasma cell neoplasms were negative for both markers.

CONCLUSIONS

A WT1/AE1/AE3 dual-color immunostain can reliably identify malignancy in pleural effusions and group malignant cells into discrete subsets, thereby narrowing the differential diagnosis. This simple double stain can be a cost-effective, first-line test in the workup of patients with malignant effusions.