SENSITIVE DETECTION OF OCCULT EWINGS CELLS BY THE REVERSE-TRANSCRIPTASE POLYMERASE CHAIN-REACTION

Recently, Ewing's tumours have been shown to carry specific hybrid tra nscripts resulting from the fusion of the EWS gene with FLI-1 or ERG g enes. Based on the sensitivity and specificity of the detection of the se alterations by the reverse transcriptase-polymerase chain reaction technique, we have developed an assay to search for small numbers of E wing cells in various sites from patients with Ewing's tumour. This me thod enables the detection of fewer than one tumour cell per million b lood mononuclear cells. A total of 28 primary sites and 51 peripheral samples from 36 patients were investigated. Tumour cells could be dete cted in 4/18 blood samples, 4/15 bone marrow aspirates and 2/18 periph eral stem cell harvests. EWS/FLI-1 and EWS/ERG transcripts being obser ved in eight and two cases respectively. The type of fusion transcript detected in peripheral site(s) was identical to that observed in the primary site. At diagnosis 5/16 patients (31%) demonstrated either cir culating tumour cells or/and occult bone marrow metastasis. After indu ction therapy, tumour cells were detected in 3/21 patients. This highl y sensitive method should be a relevant tool to allow a more accurate clinical assessment of the dissemination of Ewing's tumours.