This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Breast, Subject name: Pathology
A 65-year-old woman is found to have a 1-cm mass in the upper outer quadrant of the left breast. The most likely cause is 
Select and explain. 
A. Fibrocystic disease., B. Acute mastitis., C. Fibroadenoma., D. Carcinoma.
D: Carcinoma.
Answer: D: Carcinoma. 
Explanation: The location of the mass in the upper outer quadrant and the patient's age of 65 years suggest that the breast lesion is a carcinoma. A breast mass in a postmenopausal patient is most often a carcinoma.