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
Diagnostic feature of parathyroid carcinoma is - 
Select and explain. 
A. Cytology, B. Metastasis, C. Clinical features, D. All
B: Metastasis
Answer: B: Metastasis 
Explanation: Ans. is 'b' i.e., Metastasis "There is general agreement that a diagnosis of parathyroid carcinoma based on cytological detail is unreliable, and invasion of surrounding tissues and metastasis are the only reliable criteria".