**Core Concept**
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a genetic disorder characterized by the growth of numerous cysts in the kidneys, leading to renal enlargement, hypertension, and eventual kidney failure. The disease has a significant impact on the quality of life and mortality of affected individuals.

**Why the Correct Answer is Right**
The most common cause of death in ADPKD patients is cardiovascular disease, particularly hypertension and cardiac arrhythmias. This is due to the increased risk of cardiovascular events associated with hypertension, which is a common complication of ADPKD. The cysts themselves do not directly cause death, but the associated hypertension and cardiovascular disease can lead to cardiac failure, stroke, and other cardiovascular events.

**Why Each Wrong Option is Incorrect**
**Option A:** While cystic transformation of the kidneys is a hallmark of ADPKD, it is not the most common cause of death.
**Option B:** Renal failure is a significant complication of ADPKD, but it is not the most common cause of death.
**Option C:** While liver cysts can be present in ADPKD, they are not a major contributor to mortality.

**Clinical Pearl / High-Yield Fact**
ADPKD patients are at increased risk of developing hypertension and cardiovascular disease due to the associated renal cysts and fibrosis. Early detection and management of hypertension are crucial in reducing the risk of cardiovascular complications.

**Correct Answer:** C.