Microscopic description: The sections show features of malignant epithelioid tumour. The tumour forms trabeculae, nests with occasional acinar structures, surrounded by inflamed stroma. The tumour cells have enlarged nuclei, prominent nucleoli and moderate amounts of cytoplasm. Lymphovascular invasion is not seen. The tumour cells are CK7 positive. They are TTF-1, CK20, CDX-2 and PSA negative. This immunoprofile is non-specific. Possible primary sites include lung, upper gastrointestinal tract, biliary tract and pancreas.
Diagnosis: Omental mass biopsy: Metastatic poorly differentiated adenocarcinoma.
Supplementary report: Further immunostains have been performed after discussion at the MDM. The tumour cells are calretinin, CK5/6, mesothelin and WT1 positive (all mesothelial markers). They are BER-EP4 (adenocarcinoma marker) negative. The features are those of epithelioid mesothelioma.
Amended diagnosis: Omental mass biopsy: Epithelioid mesothelioma.