17β-estradiol-mediated elevation of peripheral white blood cell count observed during estramustine phosphate therapy for prostate cancer

Background: In 1983, Daponte et al. first reported an increase in the peripheral white blood cell (WBCs) counts of prostate cancer patients treated with estramustine phosphate (EMP) therapy.Objectives: In order to confirm Daponte’s observation, we reviewed the clinical data of prostate cancer patients treated with EMP. We also examined the association between WBC counts and 17β-estradiol levels throughout the duration of the EMP therapy.Patients and Methods: The study population comprised of 66 prostate cancer patients who were being treated with EMP. The complete blood count with a differential WBC count and the levels of serum 17β-estradiol and C-reactive protein measured during the therapy were compared with the baseline levels. The correlation between serum 17β-estradiol level and WBC count was calculated using the Pearson correlation test.Results: We observed that the total WBC and the neutrophil counts were significantly elevated during the therapy. The serum 17β-estradiol level significantly correlated with the WBC count (r2 = 0.031, P = 0.002). The granulocyte colony-stimulating factor levels measured during therapy were approximately 2-fold higher than the upper limit and decreased after cessation of the treatment (P = 0.037).Conclusions: We successfully confirmed Daponte’s observation. The increase in WBC counts was possibly attributable to elevated serum 17β-estradiol levels.