This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Teiary hyperparathyroidism is- 
Select and explain. 
A. High PO4 level with metastasis, B. Secondary hyperparathyroidism with CRF, C. Primary hyperparathyroidism with low Ca" levels, D. Secondary hyperparathyroidism with chief cell adenoma
D: Secondary hyperparathyroidism with chief cell adenoma
Answer: D: Secondary hyperparathyroidism with chief cell adenoma 
Explanation: Ans. is 'd' i.e., Secondary hyperparathyroidism with chief cell adenoma o Davidson states "In very small propoion of cases of secondary hyperparathyroidism continuous stimulation of the parathyroid may result in adenoma formation and autonomous PTH secretion. This is known as teiary hyperparathyroidism".