This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skin, Subject name: Medicine
A 19-year-old man has a pigmented skin lesion. Which of the following characteristics suggests a dysplastic nevus (atypical mole) rather than a benign acquired nevus? 
Select and explain. 
A. uniform tan color, B. located on buttock, C. 4 mm in diameter, D. 20 similar lesions on body
B: located on buttock
Answer: B: located on buttock 
Explanation: Dysplastic nevi and benign acquired nevi are both most common on sun-exposed areas such as the back. Atypical moles can occur on the scalp, breasts, and buttocks, rare areas for benign acquired nevi. Both lesions are usually associated with similar lesions (10-40 on average for benign nevi, often > 100 in the case of dysplastic nevi). Dysplastic nevi are larger (> 6 mm) and have irregular pigmentation and borders.