This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Prostate Cancer, Subject name: Surgery
A 49 year old man suffering from carcinoma of prostate was x -rayed. He showed areas of sclerosis and collapse of T10 and T11 vertebrae in x-ray. The spread of this cancer to the above vertebrae was through 
Select and explain. 
A. Sacral canal, B. Lymphatic vessels, C. Internal vertebral plexus of veins, D. Superior rectal vein
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 metastasis is possible because of valveless communication* between the periprostatic and vertebral plexus of veins.Points of importance -Most common sites * of bony metastasis for prostatic CA-: Lumbar vertebrae > Proximal femur > Pelvis Bony metastasis of prostate CA are mainly osteoblastic* and cause sclerotic lesions.