A 54-year-old man, a nonsmoker, has a nonhealing ulceration at the base of his tongue on the right side for 2 months. On examination this lesion is 1 cm in diameter with irregular borders. Biopsy of the lesion is performed and microscopic examination shows infiltrating squamous cell carcinoma. Which of the following infectious agents is most likely to be associated with this lesion?

**Core Concept**
The question is testing the association between a specific infectious agent and a type of oral cancer, specifically squamous cell carcinoma. This is related to the field of oncology and the role of viral infections in cancer development.

**Why the Correct Answer is Right**
Human papillomavirus (HPV) is a well-established cause of oropharyngeal squamous cell carcinoma (OPSCC), particularly in the tonsils and base of the tongue. HPV infection can lead to the development of cancer by promoting genetic instability and disrupting cell cycle regulation. The virus encodes for E6 and E7 proteins, which inhibit the tumor suppressor proteins p53 and Rb, respectively, leading to uncontrolled cell proliferation and tumorigenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** Epstein-Barr virus (EBV) is associated with nasopharyngeal carcinoma and Burkitt lymphoma, but not primarily with squamous cell carcinoma of the tongue.

**Option B:** Herpes simplex virus (HSV) can cause oral lesions, but it is not a known risk factor for squamous cell carcinoma.

**Option C:** Cytomegalovirus (CMV) is a common virus that can cause oral lesions, but it is not associated with squamous cell carcinoma.

**Clinical Pearl / High-Yield Fact**
HPV-associated OPSCC tends to have a better prognosis and response to treatment compared to tobacco-related squamous cell carcinomas.

**Correct Answer:** . Human papillomavirus (HPV)

✓ Correct Answer: C. Human papillomavirus (HPV)