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

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. 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 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. 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). We successfully confirmed Daponte’s observation. The increase in WBC counts was possibly attributable to elevated serum 17β-estradiol levels.