Estramustine affects bone mineral metabolism in metastatic prostate cancer

A patient with metastatic prostate cancer is described where treatment with Adriamycin (doxorubicin) and estramustine produced severe hypophosphatemia (serum phosphate level, 1.2 mg/dl), which was reversible when treatment was discontinued. Previous studies have shown no effect of Adriamycin on serum phosphate levels. A retrospective study of serial serum chemistry values was done in 15 patients treated with estramustine. A significant fall in the serum phosphate level (mean, 0.8 +/- 0.3 mg/dl) was observed during the first 6 weeks of treatment. When compared with similar patients treated with bilateral orchiectomy, estramustine-treated patients had lower levels of serum calcium, fractional excretion of calcium, serum phosphate, and renal tubular threshold for phosphate reabsorption (TmPO4/GFR). Qualitatively similar but quantitatively smaller effects were also seen in a group of patients treated with diethylstilbestrol (DES) in a dose of 1 to 3 mg daily. Estramustine appears to have significant effects on bone mineral metabolism, particularly on renal phosphate handling resulting in significant hypophosphatemia. This is probably due to an estrogenic effect.