This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
[{'content': 'Which of the following represents an example of metastatic calcification? \nSelect and explain. \nA. Old foci of tuberculosis in the lymph nodes, B. Mitral valve damaged by rheumatic fever, C. Pulmonary calcification in chronic renal failure, D. Breast cancer visible by mammography', 'role': 'user'}, {'content': 'Answer: C \nExplanation: End-stage renal failure leads to hyperparathyroidism and secondarily to hypercalcemia. The latter results in metastatic calcification. Old foci of tuberculosis, a calcified mitral valve damaged previously by rheumatic fever, and calcification within breast cancer are all examples of dystrophic calcification.', 'role': 'assistant'}]