**Core Concept**
The blood-brain barrier (BBB) is a highly selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). The BBB restricts the passage of solutes, including anticancer drugs, to prevent potentially toxic substances from entering the brain.

**Why the Correct Answer is Right**
The anticancer drug that can cross the blood-brain barrier is **Methotrexate** (MTX). MTX is a folate antagonist that inhibits dihydrofolate reductase (DHFR), an enzyme essential for DNA synthesis and cell division. Methotrexate can penetrate the BBB due to its lipophilic nature, allowing it to target CNS tumors, such as primary brain tumors or metastases from other cancers.

**Why Each Wrong Option is Incorrect**
* **Option A:** Cisplatin is a platinum-based chemotherapeutic agent that primarily targets DNA. It does not have significant ability to cross the BBB.
* **Option B:** Paclitaxel is a taxane that stabilizes microtubules, preventing cell division. It does not have inherent properties that allow it to cross the BBB.
* **Option D:** Vincristine is a vinca alkaloid that binds to tubulin, preventing microtubule formation. It is not known to cross the BBB effectively.

**Clinical Pearl / High-Yield Fact**
The ability of a chemotherapeutic agent to cross the BBB is crucial for treating CNS tumors. However, it also increases the risk of neurotoxicity, highlighting the need for careful selection and dosing of anticancer drugs in patients with CNS involvement.

**Correct Answer: C. Methotrexate**