Rodent ulcer is –
**Core Concept**
A rodent ulcer is a type of skin lesion characterized by the destruction of the skin and underlying tissue, often resulting in a crater-like appearance. It is a form of basal cell carcinoma, a common type of skin cancer that arises from the basal cell layer of the epidermis. The term "rodent ulcer" is a historical term that refers to the appearance of the lesion, which can resemble a hole or ulcer that resembles a rodent's bite.
**Why the Correct Answer is Right**
Rodent ulcers are caused by the uncontrolled growth of basal cell carcinoma cells, which invade and destroy the surrounding skin and tissue. This occurs due to mutations in the TP53 gene, which leads to the inactivation of the tumor suppressor protein p53. The lack of p53 function allows the basal cell carcinoma cells to proliferate uncontrollably, leading to the formation of a rodent ulcer. The characteristic appearance of a rodent ulcer is due to the central crater-like area of destruction, surrounded by a raised edge of tumor tissue.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because rodent ulcers are not caused by a viral infection. While some types of skin cancer, such as squamous cell carcinoma, can be caused by human papillomavirus (HPV), basal cell carcinoma is not associated with viral infection.
**Option B:** This option is incorrect because rodent ulcers are not a type of fungal infection. While fungal infections, such as ringworm, can cause skin lesions, rodent ulcers are a type of skin cancer.
**Option C:** This option is incorrect because rodent ulcers are not a type of benign skin lesion. While some skin lesions, such as moles or seborrheic keratoses, are benign, rodent ulcers are a type of skin cancer.
**Clinical Pearl / High-Yield Fact**
Rodent ulcers are often associated with sun exposure, and patients with a history of prolonged sun exposure are at increased risk of developing basal cell carcinoma. This is because UV radiation from the sun can cause mutations in the TP53 gene, leading to the development of skin cancer.
**Correct Answer: C. Basal cell carcinoma.**