The differential diagnosis of tumour cells in circulating blood

White-cell concentrates were made by a dextran sedimentation technique from the blood of 140 cases of malignant disease and 60 controls. The slides were searched for tumour cells and for other unusual cells with which they might be confused. Several million white cells were scanned in the slides from each case. Acceptable tumour cells were identified in the blood of seven patients, none of whom survived for more than a few months. These cells are illustrated, as well as various other cell types which may have been confused with malignant cells in the past. It is concluded that the cytology of white cell concentrates should be further explored before statistics about the occurrence of circulating tumour cells are accepted.