Decoy cells

Decoy cells are virally infected epithelial cells that can be found in the urine. Decoy cells owe their name to their strong resemblance to cancer cells, and may as such confuse the diagnosis of either viral infection or urothelial malignancy. Decoy cells are virally infected epithelial cells that can be found in the urine. Decoy cells owe their name to their strong resemblance to cancer cells, and may as such confuse the diagnosis of either viral infection or urothelial malignancy. Decoy cells are mostly prevalent in immunocompromised individuals, such as transplant recipients who are treated with immunosuppressive medication in order for their immune system not to reject the foreign transplanted organ. Several viruses mediated the emergence of decoy cells, amongst which cytomegalovirus and polyomavirus. Decoy cells are virus infected urothelial cells with a distinct morphology of enlarged nuclei and intranuclear inclusions. In renal transplant recipients, such cells may be found in up to 40 percent of cases. Decoy cells are clinically relevant since they may be used as a prognostic marker for clinical conditions such as polyomavirus BK-induced nephropathy in renal transplant recipients, and haemorrhagic cystitis in haematopoietic stem cell transplant recipients. Decoy cells can be seen in a urine sample through Papanicolaou staining or phase-contrast microscopy. By Papanicolaou stain, most decoy cells have an enlarged nucleus that bears a basophilic inclusion which is surrounded by chromatin that confers a ground-glass or gelatinous appearance. Sometimes the nuclear inclusion has a vesicular aspect, the chromatin may be clumped, and it may be surrounded by a halo. When decoy cells derive from the urothelium, the heavily enlarged and altered nuclei as well as the irregular shape of the cell body can mimic the changes observed in neoplastic cells. By phase-contrast microscopy, decoy cells show the same abnormalities described for stained specimens, namely, enlargement of the nucleus with a ground-glass or vesicular appearance, altered chromatin, enlarged nucleoli, the presence of a halo, and at times also cytoplasmic vacuoles. In our experience, these features make decoy cells different from tubular cells and transitional cells found in all other conditions. The only exception is represented by cells infected by cytomegalovirus, which frequently show a ‘bird's eye’ appearance.