**Core Concept**
Prostatic cancer metastasis typically involves the hematogenous and lymphatic routes, with a predilection for sites rich in bone marrow, such as the axial skeleton. The primary mechanism of spread is through the venous plexus surrounding the prostate gland, which drains into the inferior vena cava and subsequently to the heart.

**Why the Correct Answer is Right**
The correct answer is D. Bone because prostatic cancer cells can metastasize to the bone via the hematogenous route, where they implant and proliferate in the bone marrow. This is facilitated by the expression of vascular endothelial growth factor (VEGF) and other pro-angiogenic factors by prostate cancer cells. The bone microenvironment provides a fertile ground for cancer cell growth, and the resulting bone metastases can lead to significant morbidity, including pain, hypercalcemia, and pathological fractures. The axial skeleton, particularly the vertebral bodies, pelvis, and ribs, are common sites for prostatic cancer metastasis due to their rich vascular supply and high bone turnover rates.

**Why Each Wrong Option is Incorrect**
**Option A:** The liver is not a typical site for prostatic cancer metastasis, although it can occur through the lymphatic route. The liver is more commonly involved in metastatic disease from other primary sites, such as colorectal, breast, and gastric cancers.

**Option B:** The kidney is not a common site for prostatic cancer metastasis. While renal metastases can occur, they are relatively rare and more often associated with other primary malignancies, such as melanoma or clear cell renal carcinoma.

**Option C:** The lung is not a typical site for prostatic cancer metastasis, although it can occur through the hematogenous route. Prostatic cancer metastases to the lung are relatively rare and often associated with widespread disease.

**Clinical Pearl / High-Yield Fact**
Prostatic cancer metastasis to the bone is a common and devastating complication of advanced disease. The presence of bone metastases can be detected using various imaging modalities, including bone scans, CT, and MRI. Clinicians should be aware of the typical sites of bone metastasis and the associated clinical consequences to provide optimal care for patients with prostatic cancer.

**✓ Correct Answer: D. Bone**