<prompt> Diagnostic feature of parathyroid carcinoma isCytologyMetastasisClinical featuresAll  <response>: 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 