Other IHC markers are fundamental in order to distinguish between primary and metastatic tumors: thyroid transcription factor-1 (TTF-1) for the thyroid and lung (but it can be positive in strumal carcinoids), ISL-1 and PDX-1 for the pancreas, PAX8 for the thyroid, and CDX-2 and villin for the gastrointestinal tract [11,12]. Here, PAX8 is linked to metastatic neoplasm.