Autologous bone marrow support and bone disease in metastatic breast cancer

High-dose chemotherapy (HDCT) and autotransplantation of hematopoietic cells is being investigated as a therapy for either metastatic or localized high-risk breast cancer. Breast cancer has a tendency to metastasize to the bones and the bone marrow (BM) and therefore the probability of harvesting malignant cells when collecting stem cells for autotransplantation appears high. Thus, the elimination or decrease of this contamination in the transplanted product appears mandatory. Autologous peripheral blood stem cell transplantation (PBSCT) has shown significant advantages over autologous bone marrow transplantation (ABMT) in improving the feasibility of HDCT, while possible limiting the BM contamination. The transplantation of only CD34+ products may even be a further advance. The role of ex vivo purging of cancer cells has not been established in ABMT or PBSCT. The question remains if the positive selection of CD34+ products is sufficient for controlling cancer cell contamination or if this product should be purged as well. The review of the literature suggests that contamination of the bone marrow could have an impact in terms of risk or relapse and could thus play a role as a pejorative prognostic factor. These data, although not totally adequate for the autotransplantation setting, are raising concerns over the probability of reinfusing malignant cells at time of autotransplantation following HDCT. There is a tremendous need to address these concerns in the laboratory along with prospective clinical trials. Until further data is available, this risk must be taken into consideration when patients with breast cancer are treated with curative intent.