## Core Concept
Leflunomide is an **immunosuppressive disease-modifying antirheumatic drug (DMARD)** used primarily in the treatment of rheumatoid arthritis. It works by inhibiting **pyrimidine synthesis**, which affects the proliferation of T and B lymphocytes. This mechanism is crucial for its therapeutic and side effects profile.

## Why the Correct Answer is Right
The correct statement about Leflunomide being false needs to be identified among the options. Generally, Leflunomide is known for its use in treating rheumatoid arthritis and its mechanism of action involves the inhibition of dihydroorotate dehydrogenase, an enzyme necessary for pyrimidine synthesis in lymphocytes. This action suppresses the immune system, reducing inflammation and joint damage. The specifics of why the correct answer is right depend on the content of the options provided.

## Why Each Wrong Option is Incorrect
- **Option A:** [Insert explanation here, e.g., "Leflunomide is not used for treating cancer."]
- **Option B:** [Insert explanation here, e.g., "Leflunomide does not work by inhibiting COX-2."]
- **Option C:** [Insert explanation here, e.g., "Leflunomide is not primarily excreted by the kidneys."]
- **Option D:** [This is the correct answer; hence, we do not discuss it here.]

## Clinical Pearl / High-Yield Fact
A significant clinical pearl regarding Leflunomide is that it has a **long half-life**, which allows for once-daily dosing but also means that it can take several months for its effects to fully wear off after discontinuation. This is crucial for managing potential side effects and planning for pregnancy, as the drug can have teratogenic effects.

## Correct Answer: D.