Okay, let's tackle this question about anticancer drugs that can cross the blood-brain barrier. First, I need to remember which chemotherapy agents are known for penetrating the BBB. The blood-brain barrier is a protective mechanism that limits the entry of many substances into the brain, so only certain drugs can get through.

The core concept here is the pharmacokinetics of anticancer drugs, specifically their ability to cross the blood-brain barrier. The BBB is selective, allowing lipid-soluble, small molecules to pass through. So drugs that are lipophilic and have low molecular weight are more likely to cross.

Now, the correct answer in the example given is probably one of the common ones like lomustine (CCNU), which is a nitrosourea and known for crossing the BBB. Other examples include temozolomide, which is used in glioblastoma. Then there are others like etoposide or irinotecan, but I think those might not cross as effectively.

Looking at the options, if the correct answer is, say, lomustine, then the explanation would detail why it's lipophilic and how it's used in brain tumors. The wrong options might include drugs like methotrexate, which doesn't cross the BBB unless given directly into the CSF. Or maybe doxorubicin, which is less likely to penetrate the BBB.

I need to make sure each wrong option is explained clearly. For example, if an option is a drug that's water-soluble, it can't passively diffuse through the BBB. Also, some drugs are substrates for P-glycoprotein, which actively pumps them out, preventing entry into the CNS.

The clinical pearl here is that for central nervous system malignancies, the choice of chemotherapy must consider BBB penetration. Temozolomide is a high-yield fact because it's first-line for glioblastoma and crosses the BBB effectively.

Now, structuring the explanation with the required sections: Core Concept, Why Correct Answer is Right, Why Each Wrong Option is Incorrect, Clinical Pearl, and Correct Answer Line. Need to keep it concise within the character limit and use proper formatting. Also, ensure that the correct answer is clearly identified and the explanations are accurate and detailed enough for a postgraduate student preparing for exams like NEET PG or USMLE.

**Core Concept**
The blood-brain barrier (BBB) restricts entry of most substances into the central nervous system (CNS). Anticancer drugs that cross the BBB are typically small, lipophilic, or substrates for specific transporters like the monocarboxylic acid transporter (MCT). This determines their efficacy in treating CNS malignancies.

**Why the Correct Answer is Right**
Lomustine (CCNU), a nitrosourea alkylating agent, is highly lipophilic and crosses the BBB passively. It alkylates DNA, causing interstrand crosslinks, and is used for brain tumors. Its ability to penetrate the BBB makes it effective against gliomas and lymphomas.

**Why Each Wrong Option is Incorrect**
**Option A:** Methotrexate is water-soluble and cannot cross the BBB without intrathecal administration.
**Option B:** Doxorubicin is a substrate for P-glycoprotein, which actively effluxes it from the CNS

✓ Correct Answer: B. Nitrosourea