This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, 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: Parathyroid carcinomas may be circumscribed lesions that are difficult to distinguish from adenomas. Cells are usually uniform and resemble normal parathyroid cells and of enclosed in a capsule. Diagnosis of carcinoma based on cytologic detail is unreliable , and invasion of surrounding tissues and metastasis are the only reliable criteria. Ref: Robbins and cotrans 9e Pg 1102