DETECTION OF TUMOR-CELLS IN PERIPHERAL-BLOOD AND BONE-MARROW FROM EWING TUMOR PATIENTS BY RT-PCR

The Ewing family of tumours (ET) is characterised at the cytogenetic l evel by unique chromosome 22 rearrangements. The breakpoints have been cloned and were shown to fuse the EWS gene on chromosome 22 to one of two closely related ETS proto-oncogenes, FLI-1 or ERG, which reside o n chromosomes 11 and 21, respectively. The rearrangement results in th e expression of chimaeric transcripts, which can be identified by mean s of reverse transcriptase-polymerase chain reaction (RT-PCR). We appl ied this method for the monitoring of ET cells circulating in the peri pheral blood or infiltrating the bone marrow. The presence of tumour c ells could be detected with a sensitivity of 1 in 1 x 10(6) nucleated cells. When samples were kept at 4 degrees C, tumour cells could still be identified after 48 hr of storage. Positive RT-PCR signals origina ted from intact ET cells rather than from free RNA released by rupture d tumour cells. We analysed peripheral blood, bone marrow samples and peripheral blood stem cell collections from 16 ET patients. At diagnos is, bone marrow specimens collected from 6 patients and peripheral blo od specimen tested positive for EWS chimaeric RNA. During therapy tumo ur cells were detected in bone marrow aspirations obtained from 2 pati ents. Our results show that ET cells infiltrating the bone marrow or c irculating in peripheral blood can be identified by RT-PCR. The clinic al implications for the presence of ET cells in samples detected by RT -PCR at diagnosis and during therapy requires further evaluation. (C) 1995 Wiley-Liss, Inc.