CD44‐expressing undifferentiated carcinoma with rhabdoid features of the pancreas: Molecular analysis of aggressive invasion and metastasis

Carcinoma with rhabdoid features is a rare malignant tumor with a poor prognosis whose molecular mechanism for aggressive behavior is unclear. We describe an undifferentiated pancreatic carcinoma with rhabdoid features that demonstrated extensive invasion and metastasis. Examination of a 63‐year‐old man with back pain disclosed a retroperitoneal tumor with multiple metastases. Lymph node biopsy revealed an undifferentiated carcinoma of unknown origin. Intensive chemotherapy was ineffective; the patient died 3 months after initial symptoms. Autopsy showed that the tumor displaced the retroperitoneal space: it diffusely invaded and destroyed the pancreas and duodenum. Histology demonstrated tumor cells with eccentric vesicular nuclei, large nucleoli, juxtanuclear eosinophilic inclusions, and poor cell adhesion. Immunohistochemistry showed that tumor cells expressed cytokeratin and vimentin, and electron microscopy confirmed a perinuclear mass of intermediate fibrils and lipid droplets, which indicated an undifferentiated carcinoma with rhabdoid features. Tumor tissue contained hyaluronan; tumor cells strongly expressed CD 44, matrix metalloproteinase‐9, hypoxia‐inducible factor‐1α, hyaluronan synthase 2, and acyl‐ CoA :cholesterol acyltransferase 1 and had a high K i‐67 + ratio. Since hyaluronan is a ligand for CD 44, formation of CD 44‐hyaluronan complex on the cell surface activates CD 44 and this activation may explain why the tumor manifested aggressive invasion and metastasis throughout the clinical course.