Serial sections of the core biopsies show infiltration of fibrous connective tissue by poorly differentiated adenocarcinoma. This consists of irregularly shaped glandular structures lined by markedly pleomorphic cuboidal and columnar epithelial cells. These have irregularly shaped hyperchromatic and vesicular nuclei with a variable amount of pale cytoplasm. Solid aggregates of similar appearing atypical cells are also noted. Frequent mitotic figures are identified and there are foci of tumour necrosis. The features are consistent with an origin from colorectum.
DIAGNOSIS: "Left groin mass core biopsies": Infiltration of fibrous tissue by poorly differentiated adenocarcinoma with features consistent with an origin from colorectum. Immunohistochemistry shows strong nuclear staining for CDX2 in tumour cells and strong cytoplasmic staining for carcinoembryonic antigen (CEA) and cytokeratin CK20. No staining for TTF-1 or cytokeratin CK7 is seen in tumour cells. This profile indicates an origin of tumour from colorectum.