TTF1 and neuroendocrine neoplasm: However, differential diagnosis should include metastatic neuroendocrine tumors (metastases from gastrointestinal tract are usually CK20+ and CDX2+ and metastases from lungs are usually CK7+ and TTF1+), granulosa cell tumors (which is inhibin+ and calretinin+), poorly differentiated primary or metastatic adenocarcinomas (synaptophysin and chromogranin negative), Brenner tumors and androblastoma (9).