Caecal adenocarcinoma with rhabdoid phenotype: an immunohistochemical and ultrastructural analysis.

A polypoid caecal adenocarcinoma in a 72-year-old female was found microscopically to be composed mainly of rhabdoid cells. Deposits in the liver and lymph nodes had a similar histological appearance to the primary tumour. The rhabdoid cells were typified by abundant eosinophilic cytoplasm, eccentric nuclei and prominent nucleoli. The differential diagnosis included rhabdomyosarcoma, metaplastic carcinoma (carcinoma with sarcomatoid dedifferentiation), carcinosarcoma and extra-renal rhabdoid tumour. The rhabdoid cells showed strong immunoreactivity with cytokeratin, epithelial membrane antigen and vimentin. Ultrastructurally, cytoplasmic whorls of intermediate filaments were noted. Multiple sections, immunohistochemistry and ultrastructural examination all revealed an adenocarcinomatous component which blended with the rhabdoid areas. In one area a rhabdoid cell was present within a malignant gland. This case illustrates that the rhabdoid appearance of many tumours can be misleading and is merely a non-specific morpho-phenotypic pattern seen in extra-renal sites. In the extra-renal setting, careful search for evidence of differentiation should be undertaken.