**Core Concept**
The definitive diagnosis of oral cancer involves histopathological examination of a biopsy specimen to identify malignant cells. This is crucial for planning appropriate treatment and predicting patient outcomes.

**Why the Correct Answer is Right**
The correct answer involves histopathological examination of a biopsy specimen, which allows for the identification of malignant cells, including their morphology, growth patterns, and invasion into surrounding tissues. This is essential for distinguishing oral cancer from benign lesions or precancerous conditions. The biopsy specimen is typically stained with hematoxylin and eosin (H&E) and examined under a microscope by a pathologist.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because imaging studies, such as CT or MRI scans, can help identify oral cancer but do not provide a definitive diagnosis.
**Option B:** This option is incorrect because clinical examination and patient history can raise suspicion of oral cancer but are not sufficient for a definitive diagnosis.
**Option C:** This option is incorrect because molecular biomarkers, such as p53 mutations, can be associated with oral cancer but are not used as the sole criterion for diagnosis.

**Clinical Pearl / High-Yield Fact**
The American Joint Committee on Cancer (AJCC) staging system is used to classify oral cancer based on tumor size, depth of invasion, lymph node involvement, and distant metastasis.

**Correct Answer:** C. Histopathological examination of a biopsy specimen.