PERIPHERAL-BLOOD STEM-CELL MOBILIZATION FOR HEMATOPOIETIC SUPPORT OF RADIOIMMUNOTHERAPY IN PATIENTS WITH BREAST-CARCINOMA

BACKGROUND, In clinical trials of radiolabeled monoclonal antibodies t argeting metastatic breast carcinoma, myelosuppression has been the in itial dose-limiting toxicity. We previously have shown that mobilized peripheral blood stem cell transfusions ameliorate this toxicity of ra dioimmunotherapy (RIT). Because of the difficulty we experienced harve sting adequate numbers of precursor cells from some of these heavily p retreated patients, we have compared the mobilization results and clin ical histories of the metastatic breast carcinoma patients referred fo r RIT with those of metastatic breast carcinoma patients referred for high dose chemotherapy (HDCT) with transplantation. METHODS. Mobilizat ion of stem cells into the peripheral blood was accomplished using gra nulocyte-colony stimulating factor with or without chemotherapy. Granu locyte macrophage colony-forming assays (CFU-GM) and flow cytometric a nalysis for CD34 positive cells were used to evaluate the number of he matopoietic precursors mobilized and collected with each apheresis pro cedure. Clinical characteristics, including prior chemotherapy and ext ernal beam radiotherapy, tumor bulk, and performance status, were dete rmined by chart review. RESULTS. Significantly fewer hematopoietic pre cursors (both CD34 positive cells and CFU-GM) were harvested per proce dure from the six RIT patients compared with a group of six patients w ith metastatic breast carcinoma who had stem cells harvested prior to HDCT (P = 0.002). There was no significant difference between the grou ps with regard to age or prior radiotherapy. All the RIT patients had received more chemotherapy, had a less favorable performance status (1 vs. 0), and had measurable tumor, whereas all the HDCT patients had m inimal residual disease. CONCLUSIONS, Patients enrolled in RIT studies had lower stem cell yields than metastatic breast carcinoma patients scheduled to receive HDCT with stem cell transplantation. Poor mobiliz ation is unlikely to be due to the mobilizing regimen alone and may be related to the intensity of prior therapy and/or tumor bulk. Mobilizi ng adequate stem cells for multiple treatment cycles from patients on Phase I/II RIT trials may require new, more effective mobilizing regim ens, but referral of patients earlier in their disease course, prior t o chronic bone marrow damage and disease progression, is recommended s trongly. (C) 1997 American Cancer Society.