**Core Concept**
Bcl-2 is a key protein involved in the regulation of apoptosis, or programmed cell death. It is a member of the Bcl-2 family, which plays a crucial role in maintaining the balance between life and death of cells. Bcl-2 acts as an anti-apoptotic protein by inhibiting the activation of caspases, a group of enzymes responsible for executing cell death.

**Why the Correct Answer is Right**
Bcl-2 functions by binding to and inhibiting the pro-apoptotic proteins Bax and Bak, thereby preventing their oligomerization and subsequent activation of the mitochondrial outer membrane permeabilization (MOMP). This prevents the release of cytochrome c from the mitochondria, which is a crucial step in the activation of the caspase cascade and ultimately, cell death. The overexpression of Bcl-2 has been implicated in various cancers, including follicular lymphoma, where it leads to uncontrolled cell growth and tumor formation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a correct description of Bcl-2's function.
**Option B:** Bcl-2 is not a pro-apoptotic protein; it is anti-apoptotic.
**Option C:** This option is not a correct description of Bcl-2's relationship to cancer.

**Clinical Pearl / High-Yield Fact**
Bcl-2's anti-apoptotic function can be exploited therapeutically in cancer treatment, and its expression is often used as a prognostic marker in various malignancies.

**Correct Answer: B. Anti-apoptotic protein.**