**Core Concept**
The abscopal effect is a phenomenon where localized radiation therapy to a specific tumor site leads to systemic anti-tumor effects, potentially causing regression of distant metastases. This effect is thought to be mediated by the immune system.

**Why the Correct Answer is Right**
The abscopal effect is most commonly associated with renal cell carcinoma (RCC). The exact mechanism is not fully understood, but it is believed to involve the release of tumor antigens and danger signals from the irradiated tumor, which stimulate a systemic immune response against distant tumor cells. This immune response is often characterized by the activation of T cells and the production of cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α).

**Why Each Wrong Option is Incorrect**
**Option A:** Melanoma - While melanoma can exhibit a range of immune-related effects, it is not typically associated with the abscopal effect.
**Option B:** Breast cancer - Breast cancer can respond to radiation therapy, but it is not commonly linked to the abscopal effect.
**Option C:** Lung cancer - Lung cancer can exhibit a range of immune-related effects, but it is not typically associated with the abscopal effect.

**Clinical Pearl / High-Yield Fact**
The abscopal effect is a rare but potentially powerful therapeutic strategy for patients with advanced cancer. It highlights the importance of the immune system in cancer treatment and the potential for localized therapies to have systemic effects.

**Correct Answer: C. Renal cell carcinoma.**