Normal serum alkaline phosphatase in the presence of extensive skeletal metastases of prostate cancer

ABSTRACT

Alkaline phosphatase [ALP] is a nonspecific tumor marker as it is neither organ or tumor specific. An elevation of the enzyme in relation to carcinoma of the prostate is usually due to boene or liver involvement, or both, by metastatic disease. We report the case of a 91-year-old man who presented with chronic urinary retention. Investigations revealed prostate specific antigen [PSA] of 831.4 ng/ml, biochemical evidence of moderate renal impairment, normal liver function tests and normal alkaline phosphatase. Whole body skeletal scintigraphy with 99mTC-MDF showed widespread skeletal metastases. Transrectal ultrasound of the prostate revealed a 40 gm prostate gland with a hypoechoic defect in the periphery of the gland. Prostate biopsy revealed prostate cancer [Gleason's score 8]. Total serum testosterone, zinc and magnesium were below the normal range. Bone densitometry revealed osteoporosis. Channel transurethral resection of the prostate was performed together with bilateral orchidectomy. Testicular histology revealed atrophic tests. Normal serum alkaline phospatase in this patient in the presence of extensive skeletal metastases may be due to the combination of the following factors relative hypogonadism, osteoporosis, low serum zinc and magnesium. This case report may provide a possible explanation for the observation that about 10% of men with widespread skeletal metastases from prostate cancer may not have elevated serum alkaline phosphatase