**Core Concept**
The phenomenon of spontaneous regression of malignant tumors is a rare occurrence where a tumor decreases in size or disappears without any treatment. This is often observed in certain types of neoplasms, such as neuroblastomas and renal cell carcinomas, and is believed to be due to an overactive immune response or other mechanisms that counteract tumor growth.

**Why the Correct Answer is Right**
Spontaneous regression of malignant tumors is thought to occur due to an overactive immune response, where the body's immune system is able to recognize and attack cancer cells. In some cases, this may be due to the production of cytokines, such as interferon-gamma, which can stimulate the immune system to target cancer cells. Additionally, certain types of tumors may be more susceptible to spontaneous regression due to their genetic makeup or the presence of specific molecular markers.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe a tumor type that is known to exhibit spontaneous regression.
**Option B:** This option is incorrect because it refers to a different medical condition altogether, and is not related to the spontaneous regression of malignant tumors.
**Option C:** This option is incorrect because it is a type of treatment for cancer, rather than a tumor type that exhibits spontaneous regression.

**Clinical Pearl / High-Yield Fact**
One notable example of spontaneous regression of a malignant tumor is the case of neuroblastoma, a type of cancer that arises in the adrenal glands. In some cases, neuroblastoma has been known to spontaneously regress, and this phenomenon is often associated with a favorable prognosis.

**Correct Answer:** C Melanoma