**Question:** Which of the following statements about a basal cell carcinoma of the skin is TRUE?

A. It is the most common malignant skin tumor.
B. It is caused by UV radiation exposure.
C. It presents as a single, painless nodule.
D. It typically affects elderly patients only.

**Core Concept:** Basal cell carcinoma (BCC) is a type of skin cancer that originates from basal cells of the epidermis. It is a malignant tumor, but not the most common in terms of overall malignancies. UV radiation exposure contributes to its development but is not the sole cause.

**Why the Correct Answer is Right:** BCC is indeed the most common malignant skin tumor, making up approximately 80% of all skin cancers in the United States. However, it is essential to recognize that other types of skin cancers, such as squamous cell carcinoma (SCC) and melanoma, are also common but less frequent than BCC.

**Why Each Wrong Option is Incorrect:**

A. **False:** BCC is not the most common malignant tumor overall, but it is the most common type of skin cancer.
B. **True:** UV radiation exposure increases the risk of BCC development, but it is not the sole cause, as other environmental and genetic factors also contribute.
C. **False:** BCC can present as a single, painless nodule, but it often occurs in sun-exposed areas of the body and presents with various clinical features, including pearly, pearl-like lesions, ulcerated lesions, or as a scaly plaque.
D. **False:** BCC can occur in any age group, although the risk increases with age, especially in individuals with fair skin types. Elderly patients are more likely to present with advanced disease due to prolonged sun exposure over a lifetime.

**Clinical Pearl:** It is crucial for clinicians to be aware of the diverse clinical presentations of BCC to facilitate early detection and appropriate management to prevent progression and potential complications, such as bone or cartilage destruction and local tissue invasion.

**Correct Answer:** D. Basal cell carcinoma typically affects elderly patients, as the risk increases with age, especially in individuals with fair skin types.

**Why Each Wrong Option is Incorrect:**

A. **False:** BCC can present in any age group, making this statement incorrect.
B. **False:** While UV radiation exposure increases the risk of BCC, it is not the sole cause, as other factors, including genetic predispositions, contribute to its development.
C. **False:** BCC can present with various clinical features, not just a single, painless nodule.
E. **False:** BCC does not exclusively occur in sun-exposed areas; it can arise in any skin type and can present in non-sun-exposed areas as well.