Tumor cells are present in stem cell harvests of Ewings sarcoma patients and their persistence following transplantation is associated with relapse

Background. Tumor cells frequently contaminate autologous stein cell products in a variety of malignancies, but their clinical significance remains controversial. We retrospectively monitored tumor contamination in stem cell harvests from patients with Ewing family of tumors (EFT) all harboring the specific translocation EWS-FLI-1 that characterize these tumors. Procedure. Twenty-seven harvests from 11 patients were included in the study. In addition, 6 and 19 bone marrow (BM) or peripheral blood (PBL) samples were available before and after transplantation, respectively, for RT-PCR and nested PCR analyzes. Results. All 11 patients had contaminating tumor cells in their harvests. All samples prior to transplantation were RTPCR positive. Two out of the 11 patients who underwent transplantation died of complications. Out of the remaining nine patients, two are alive and well 68 and 84 months from diagnosis, and are the only patients with no detectable tumor cells in their samples after transplantation. One of these patients harbored contaminating tumor cells in only one of the two harvests collected. Seven patients relapsed after transplant, and in four patients BM/PBL samples were available prior to the clinical relapse. All these samples harbored contaminating tumor cells. Conclusions. We suggest a possible correlation between the amount of contaminating cells in the harvest and relapse after transplantation. Quantitative RT-PCR studies of the chimeric transcripts are underway to explore this issue.