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This conference was held on June 23–25, 1996, at the Kunstlerhaus, Munich, Germany, and was sponsored by the International Society for Hematotherapy and Graft Engineering, as well as AMGEN...

We have developed a multiassay system consisting of fluorescence microscopy, immunocytology and tumor colony assay to monitor the removal of tumor cells from bone marrow. This system was tested in preclinical purging experiments in which neuroblastoma cells were seeded into bovine marrow and purged by treatment with monoclonal antibodies and immunomagnetic beads. Eight experiments were performed on two different neuroblastoma cell lines seeded at 2% and/or 5% contamination. We consistently demonstrated greater than a 3 log removal with one cycle of antibody/bead treatment and greater than a 1 log further reduction by addition of a second cycle. We also demonstrated removal of all detectable tumor stem cells by this purging method. We feel that this system will prove valuable for monitoring ex vivo tumor removal in future clinical studies and should be considered for use in other purging trials.

Patients undergoing high-dose chemotherapy (HDC) with autologous stem cell rescue (ASCR) may have tumor cells inadvertently infused if their stem cell product is tumor contaminated. We used an immunocytochemical (ICC) method to analyze 31 histologically negative bone marrow (BM) specimens taken from women with advanced-stage breast cancer at the time of BM harvest before HDC. All 31 patients were treated on one of three consecutive HDC protocols and received BM or BM and peripheral stem cells (PSC) as ASCR. Six of 26 evaluable patients had ICC-detectable contaminating tumor cells in their BM harvests. These 6 patients had a trend toward decreased overall survival compared with those patients without ICC-detectable tumor cells (17 months median versus 25+ months, p = 0.11, log rank test for those patients achieving complete response, CR, from HDC). The sites of relapse in the ICC-positive and ICC-negative groups were not notably different when analyzed for new sites versus previous sites of disease. Therefore, our retrospective analysis of a small cohort of patients suggests that the infusion of tumor cells in breast cancer patients undergoing HDC may confer a poor prognosis. Relapse patterns however suggest failure both in new sites and in sites of previous disease. Additional studies in expanded patient populations are needed to explore further the role of tumor cell infusion in ASCR and the possible clinical benefits of tumor cell removal procedures.

Peripheral blood stem cell (PBSC) reinfusions are being used with increasing frequency in lieu of, or in addition to, autologous bone marrow transplantation (ABMT) to rescue cancer patients from the myeloablative effects of high-dose chemotherapy. However, the incidence and quantity of tumor cell contamination in PBSC collections has not been widely investigated. This paper reviews the existing data and presents new information to demonstrate that tumor cells are detectable in PBSC harvests from patients with a variety of malignancies. Furthermore, their presence in peripheral blood may have prognostic and clinical significance. Areas of future research and applications for PBSC technologies are also discussed.