Although autologous PBPC transplantation is being used increasingly for the treatment of breast cancer, there are few data on factors influencing mobilization and engraftment in these patients. We have analyzed these factors in 70 patients with advanced or metastatic breast cancer undergoing autologous PBPC transplantation. All patients were mobilized after stimulation with G-CSF, and a median of 3.16 x 10(6)/kg CD34+ cells (range 0.75-23.33) were infused. All patients received conditioning with a combination of cyclophosphamide, thiotepa, and carboplatin, and postinfusion G-CSF was administered to 60 patients. The median times to reach 0.5 x 10(9)/L and 1 x 10(9)/L neutrophils were 10 and 11 days, respectively. The median times to obtain 20 x 10(9)/L and 50 x 10(9)/L platelets were 12 and 18 days, respectively. An analysis of factors that influence CD34+ cell collection was performed by linear regression. Previous radiation therapy and increasing age were associated with lower numbers of CD34+ cells collected. Those variables that could influence the tempo of engraftment were examined by multivariate analysis using Cox regression models. The number of CD34+ cells infused was found to influence both neutrophil and platelet recovery. The use of G-CSF after transplant, accelerated neutrophil recovery, and having more than six cycles of previous chemotherapy was an unfavorable factor for recovering50 x 10(9)/L platelets.