The analysis performed by Dr Schrama and colleagues of day 15 absolute lymphocyte count (ALC) recovery in metastatic breast cancer patients after autologous stem cell transplantation is important and appreciated, since it is the first evaluation of our findings1 by another group of investigators. Despite the fact that Dr Schrama's analysis does not demonstrate a survival difference between cohorts of patients achieving an ALC ≥500 cells/μl on day 15 post-transplant vs those that do not (ALC <500 cells/μl cohort), we agree with Dr Schrama's conclusion that both our studies are too small to definitively ascertain the prognostic value of day 15 ALC. Appropriately powered, larger studies are required to ascertain the prognostic impact of day 15 ALC recovery in patients with metastatic breast cancer, as we had previously reported in patients with multiple myeloma and non-Hodgkin's lymphoma.2 Even though no difference in the median time to progression was observed in Dr. Schrama's account, it is interesting to point out that the survival curve for patients with ALC ≥500 cells/μl appears to plateau compared with no plateau for patients with ALC <500 cells/μl.
Dr Schrama and colleagues also raised a very important question of the role of the reinfusion of lymphocytes on immune recovery and clinical outcome postautologous stem cell transplantation. We have recently submitted a manuscript on 550 patients describing the direct impact of the infused autograft ALC not only on immune recovery, but also on clinical outcome after autologous stem cell transplantation. This is relevant in view of our metastatic breast cancer data discussed herein, because some patients in that study were mobilized with growth factor alone and others with Flt-3 ligand. The different stem cell mobilization regimens may have an impact on different subsets of lymphocytes collected during stem cell harvests, possibly differentially affecting immune cell subset recovery and perhaps clinical outcome after autologous stem cell transplantation. Therefore, we agree with Dr Schrama and colleagues that further investigation on the role of immune system recovery on survival after autologous stem cell transplantation is warranted, and we wholeheartedly encourage their further work in this field.
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