['Some transplant-related complications, such as the engraftment syndrome, are thought to be mediated by cytokines released during expansion of hematopoietic progenitors at the time of neutrophil recovery. Since there is an inverse correlation between CD34(+) cell dose and time to neutrophil recovery, we sought to determine if peritransplant toxicity and early mortality were adversely affected by high CD34(+) cell doses.', 'The study group included 186 women with breast cancer who received high-dose cyclophosphamide, carmustine, thiotepa and an autologous PBSC transplant. The median CD34(+) cell dose was 5.9 x 10(6)/kg (1.0-154.7 x 10(6)/kg). Patients were categorized by CD34(+) cell dose (1.0-3.5, 3.6-5.9, 6.0-19.9, and 20.0-154.7 x 10(6)/kg) for assessment of outcomes.', 'Grades 2-4 mucositis occurred in 49%, cardiac toxicity in 7%, pulmonary toxicity in 5%, cystitis in 4%, diarrhea in 3%, renal toxicity in 1%, and central nervous system toxicity in 1%. A Grade 2-4 regimen-related toxicity occurred in 109 patients (59%) and Grade 3-4 in eight patients (4%). Overall survival was 100% at Day 30, 96% at Day 90, and 89% at 1 year. Treatment-related mortality was 3.8%. In multivariate analyses that included prior chemotherapy, disease status, visceral metastases, prior chest radiation and age, CD34(+) cell dose group was not an independent risk factor for Grade 2-4 mucositis, Grade 2-4 maximum toxicity, Grade > or =3 cumulative toxicity, 90 day survival or 1 year survival.'] Do high CD34 cell doses worsen regimen-related toxicity or early mortality after autologous blood stem cell transplantation for breast cancer?