Initial clinical attempts that aimed to enrich for a phenotypically defined, HSC-enriched CD34+ subpopulation for autologous transplantation in humans were performed in the 1990s.41–43 Flow-based cell sorting HSC-enrichment strategies focused on lin−CD34+CD90+ or CD34+CD90+ cell fractions that were phenotypically depleted of malignant cells and were evaluated in autologous stem cell transplants for the treatment of multiple myeloma, breast cancer, and non-Hodgkin lymphoma.41–43 Rapid and sustained engraftment were seen in patients affected by multiple myeloma and breast cancer. This evidence concerns the gene THY1 and breast cancer.