Question

a 70 - year - old male with a history of prostate carcinoma presents with dull, aching low back pain. imaging reveals multiple osteoblastic lesions in the lumbar vertebrae. which laboratory enzyme is most useful for confirming that his prostate cancer has metastasized to bone?
a) alkaline phosphatase
b) creatine phosphokinase
c) aspartate aminotransferase
d) prostatic specific antigen
e) prostatic acid phosphatase

Explanation:

• Alkaline phosphatase (ALP): Osteoblasts (cells involved in bone formation) produce ALP. In cases of bone metastasis (especially osteoblastic lesions as seen in prostate cancer bone metastasis), the activity of osteoblasts increases, leading to an elevation in serum ALP levels.
• Creatine Phosphokinase (CPK): Primarily found in muscle (skeletal, cardiac) and brain. Elevated in muscle - related disorders (e.g., rhabdomyolysis, myocardial infarction) or brain injury, not specific for bone metastasis.
• Aspartate Aminotransferase (AST): Present in liver, heart, skeletal muscle, etc. Elevated in liver diseases (e.g., hepatitis, cirrhosis), myocardial infarction, or muscle damage, not relevant for bone metastasis confirmation.
• Prostatic Specific Antigen (PSA): A marker for prostate cancer (both local and metastatic disease), but not specific for bone metastasis. It can be elevated in non - metastatic prostate cancer (e.g., early - stage prostate cancer with no bone involvement).
• Prostatic Acid Phosphatase (PAP): Another prostate - specific marker, but its use has been largely replaced by PSA. Also not specific for bone metastasis.

Answer:

A. Alkaline phosphatase