Detection of circulating tumor cells in patients with Ewing's sarcoma and peripheral primitive neuroectodermal tumor

To determine the feasibility of detecting Ewing's sarcoma (ES) or peripheral primitive neuroectodermal tumor (PNET) through a reverse-transcriptase polymerase chain reaction (RT-PCR) of the t(11;22)(q24;q12) fusion transcript in blood and bone marrow samples from patients with these neoplasms.

Peripheral-blood (PB) and/or bone marrow aspirate (BM) samples were obtained from 28 patients with ES or PNET at initial presentation or at relapse. Patients were divided into two groups: newly diagnosed patients with nonmetastatic disease and those with metastatic/relapsed disease. RNA was extracted from fractionated BM and PB samples, and RT-PCR was performed for the EWS/HumFLI1 fusion mRNA was transcribed across the t(11;22) breakpoint.

Among the 16 patients with nonmetastatic disease, three of 16 were RT-PCR positive for EWS/HumFLI1 RNA in BM and three of 10 were positive in PB. The total number of nonmetastatic patients who were positive in either PB or BM was four of 16 (25%). Among patients with metastatic/relapsed disease, two of six were positive in BM and five of 10 were positive in PB. The total fraction of patients with metastatic/relapsed disease that was positive in either BM or PB was six of 12 (50%).

In this study, we show that it is possible to amplify the EWS/HumFLI1 RNA by RT-PCR from the BM and PB of a subset of patients with both nonmetastatic and metastatic ES or PNET, which implies that occult tumor cells are present at these sites. The true biologic and clinical meaning of this information is unknown. However, it does suggest a possible application of RT-PCR for the monitoring of residual disease in patients who are undergoing therapy for ES or PNET. This approach may permit early identification of patients who may benefit from alternative therapy or who may be spared possible overtreatment.