**Core Concept**
Malignant melanoma is a type of skin cancer characterized by an uncontrolled proliferation of melanocytes, the pigment-producing cells in the epidermis. The vertical growth phase is a critical stage in the development of melanoma, where the tumor invades deeper into the skin.

**Why the Correct Answer is Right**
Melanomas that exist solely in the vertical growth phase are typically referred to as "radial growth phase" melanomas. These tumors have not yet invaded the dermis and are confined to the epidermis. They are characterized by a horizontal growth pattern, with the tumor cells spreading out in a radial fashion. In contrast, melanomas that have invaded the dermis are in the vertical growth phase, with the tumor cells growing upwards into the deeper skin layers.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the growth phase of the melanoma.
**Option B:** This option is incorrect because it refers to a different type of skin cancer, not melanoma.
**Option C:** This option is incorrect because it describes a melanoma that has invaded the dermis, indicating a vertical growth phase.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that melanomas can be classified into two main types based on their growth phase: radial growth phase (confined to the epidermis) and vertical growth phase (invading the dermis). Understanding this distinction is crucial for accurate diagnosis and treatment planning.

**Correct Answer:** B.