Stability of white blood cell counts following standard radiation approaches for high-risk adenocarcinoma of the prostate: Implications for combination therapy.

201 Background: Traditional wisdom has suggested that under some circumstances radiation therapy may be immunosuppressive, thus obviating effective combination approaches with immunotherapy. Our purpose was to test whether standard radiation therapy for high-risk prostate cancer are immune modulating, thereby prohibiting potential combination with cellular based immunotherapies such as sipuleucel-T. Methods: Retrospective analysis of complete blood count with differential (CBC) data was performed on 26 patients with high-risk adenocarcinoma of the prostate undergoing external beam radiation therapy between January 2008 and November 2010. CBC data were collected prior to radiation therapy and at up to 4 time points thereafter, and compared to normal ranges from an outside reference lab (WBC 3,800-10,700/μL; ALC 910-4,280/μL). Results: The median age was 73 (range 62-86), and 16 patients were on concurrent androgen deprivation therapy. Patients received intensity modulated, dose-escalated external beam radiotherapy. Baseline and subsequent median white blood counts (WBC) and absolute lymphocyte counts (ALC) remained within the normal ranges. In the clinically relevant time frame of <3 months following radiation therapy where sipuleucel-T could be considered, the WBC and ALC were 5,350 and 970, respectively. The median WBC and ALC then gradually increased to 5,800 and 1,250, respectively, at 6-12 months post radiation therapy. Conclusions: These data suggest that in the setting of external beam radiation approaches for high-risk adenocarcinoma of the prostate, no significant changes in either WBC or ALC were observed. The hematologic status in these patients remained stable, suggesting that combination radiation / cellular based immunotherapy approaches are feasible. Further analysis is warranted to test the potential of novel immunotherapeutic agents with radiation therapy. [Table: see text]