**Core Concept**
Malignant melanoma is a type of skin cancer characterized by the uncontrolled growth of melanocytes, which are pigment-producing cells in the skin. The most common cause of death in malignant melanoma is due to the metastasis of cancer cells to distant organs, particularly the brain, lungs, liver, and bones.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of metastasis in malignant melanoma. Cancer cells from the primary melanoma can break away from the original tumor site, enter the bloodstream, and travel to distant organs, where they can establish new tumors. This process is facilitated by the expression of specific adhesion molecules and the ability of cancer cells to evade the immune system. The brain is a common site for metastasis due to its rich blood supply and the presence of specific receptors that allow cancer cells to adhere to endothelial cells.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while local recurrence is a common complication of malignant melanoma, it is not the most common cause of death.
* **Option B:** This option is incorrect because although lymph node metastasis is a significant prognostic factor in malignant melanoma, it is not the most common cause of death.
* **Option C:** This option is incorrect because while distant metastasis is the most common cause of death in malignant melanoma, it is not specific to the brain.

**Clinical Pearl / High-Yield Fact**
The presence of brain metastases in malignant melanoma is a poor prognostic sign, and patients with this condition typically have a median survival time of less than 6 months.

**Correct Answer: C. Brain metastasis**