## **Core Concept**
The TNM staging system is widely used for classifying the extent of spread of cancer, including oral cancer. The 'T' classification refers to the size and extent of the primary tumor. For oral cancer, the T classification helps in determining the prognosis and treatment plan.

## **Why the Correct Answer is Right**
The correct classification for T3 in oral cancer is a tumor more than 4 cm in greatest dimension. This classification is crucial for treatment planning and prognosis. The T3 category indicates a larger tumor size, which may require more aggressive treatment approaches.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Tumor limited to one site, this description does not match T3 criteria.
* **Option B:** Tumor more than 2 cm but not more than 4 cm in greatest dimension, this corresponds to T2.
* **Option D:** Tumor invading adjacent structures, this description could fit T4 but not T3.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the TNM staging system helps in standardizing cancer treatment and prognosis. For oral cancer, T3 specifically refers to a tumor size greater than 4 cm, which significantly impacts the treatment plan and patient outcome.

## **Correct Answer:** . Tumor more than 4 cm in greatest dimension.