**Core Concept**
The paranasal sinuses are a group of air-filled cavities located within the bones of the skull, and they are lined by mucous membranes that can give rise to malignant tumors. The most common type of cancer affecting these sinuses is squamous cell carcinoma.

**Why the Correct Answer is Right**
The maxillary sinus is the largest of the paranasal sinuses and is located in the maxilla bone, which forms the upper jaw. It is in close proximity to the oral cavity and the nasal cavity, making it more susceptible to carcinogens and carcinogenic exposure. The maxillary sinus has a larger surface area and more mucous membrane lining, which increases its risk of developing cancerous changes. The maxillary sinus is also more commonly exposed to smoking and other environmental carcinogens, further increasing its risk of malignancy.

**Why Each Wrong Option is Incorrect**
**Option A:** The frontal sinus is less commonly affected by carcinoma due to its smaller size and less exposure to carcinogens.
**Option B:** The ethmoid sinuses are a group of small sinuses located between the nasal cavity and the maxillary sinuses, and while they can be affected by cancer, they are less commonly involved than the maxillary sinus.
**Option D:** The sphenoid sinus is the smallest of the paranasal sinuses and is located in the sphenoid bone, which forms the base of the skull. It is less commonly affected by carcinoma due to its smaller size and less exposure to carcinogens.

**Clinical Pearl / High-Yield Fact**
The maxillary sinus is also the most common site of inverted papilloma, a benign tumor that can be malignant in up to 10% of cases. Inverted papilloma is often associated with a history of smoking and exposure to environmental carcinogens.

**✓ Correct Answer: C. Maxillary**