MUC5AC and papillary cystadenocarcinoma: 2,3 Papillary carcinoma of the thyroid shows characteristic nuclear features and expresses nuclear positivity for thyroid transcription factor 1 (TTF-1). Mucinous adenocarcinoma and intestinal-type adenocarcinoma are two other uncommon subtypes of adenocarcinoma-NOS, which need to be differentiated from papillary cystadenocarcinoma as these tumors have an aggressive clinical course.3 Histopathologically, mucinous adenocarcinoma is characterized by large pools of extracellular mucin and immunopositive for CK 7. Intestinal-type adenocarcinoma is positive for CK 20 and CDX2.2,3