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
Tertiary hyperparathyroidism is- 
Select and explain. 
A. High PO
4
 level with metastasis, B. Secondary hyperparathyroidism with CRF, C. Primary hyperparathyroidism with low Cam' levels, D. Secondary hyperparathyroidism with chief cell adenoma
D: Secondary hyperparathyroidism with chief cell adenoma
Answer: D: Secondary hyperparathyroidism with chief cell adenoma 
Explanation: Davidson states "In very small proportion of cases of secondary hyperparathyroidism continuous stimulation of the parathyroid may result in adenoma formation and autonomous PTH secretion. This is known as tertiary ​hyperparathyroidism".