**Core Concept**
Malignant melanoma is a type of skin cancer characterized by the uncontrolled growth of melanocytes, which are pigment-producing cells. The prognosis of malignant melanoma is influenced by several factors, primarily the thickness of the tumor, the presence of ulceration, and the involvement of lymph nodes.

**Why the Correct Answer is Right**
The prognosis of malignant melanoma is determined by the Breslow thickness, which measures the depth of the tumor in millimeters, and the Clark level, which describes the extent of tumor invasion into the skin. The Breslow thickness is a critical factor in determining the prognosis, as thicker tumors are associated with a poorer outcome. The presence of ulceration also negatively impacts the prognosis, as it indicates a higher risk of metastasis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while tumor location can influence the prognosis, it is not the primary factor determining the outcome of malignant melanoma.
* **Option B:** This option is incorrect because while age can be a prognostic factor in some cancers, it does not play a significant role in determining the prognosis of malignant melanoma.
* **Option D:** This option is incorrect because while the presence of metastasis is a critical factor in determining the prognosis, it is not the only factor, and the Breslow thickness and ulceration are also important.

**Clinical Pearl / High-Yield Fact**
The "ABCD rule" can be remembered to determine the prognosis of malignant melanoma: A (asymmetry), B (border irregularity), C (color variation), and D (diameter > 6mm). If any of these features are present, the tumor is more likely to be malignant.

**Correct Answer:** C.