This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
A 50-year-old man suffering from carcinoma of prostate showed areas of sclerosis and collapse of T10 and Til vertebrae in X-ray. The spread of this cancer to the above vertebrae was most probably through: 
Select and explain. 
A. Sacral canal, B. Lymphatic vessels, C. Internal vertebral plexus of veins, D. Superior rectal veins
C: Internal vertebral plexus of veins
Answer: C: Internal vertebral plexus of veins 
Explanation: Ans. is 'c' i.e. internal vertebral plexus of veins Prostatic cancer spreads to the bones through blood vessels; first into the periprostatic venous plexus and then into the internal vertebral plexus of veins. This metastatic is possible because of valveless communication* between the periprostatic and vertebral plexus of veins. Points of importance - Most common sites* of bony metastatic for prostatic CA-: Pelvis > Lumbar vertebra > thoracic vertebra > head of the femur > the ribs > the humerus (Note that both Bailey and S.Das agree that pelvis* is the most common site for bony metastasis) Bony metastasis of prostate CA are mainly osteoblastic* and cause sclerotic lesions.