Mucin production in metastatic papillary carcinoma of the thyroid

Although textbooks often state that demonstration of mucin in a metastatic carcinoma excludes the possibility of a thyroidal primary tumor, mucin recently has been reported in various types of thyroid carcinoma, particularly medullary carcinoma. The presence of mucin in papillary carcinoma has not been extensively studied, even though this tumor not uncommonly presents with lymph node metastasis. We stained 40 lymph nodes containing metastatic papillary carcinoma of the thyroid for mucin. Mucin was demonstrable by mucicarmine stain in the colloid, luminal borders, and cytoplasm in 18 (45%), 9 (22.5%), and 7 (17.5%) cases respectively; 17 cases (42.5%) were completely negative. With alcian blue staining, mucin was seen in 9 (22.5%), 9 (22.5%), and 7 (17.5%) cases; 25 cases (62.5%) were negative. Most of the cytoplasmic vacuoles were target-like, with a peripheral rim of sulfated acid mucin and a central core of neutral mucin. The psammoma bodies stained consistently with mucicarmine, alcian blue, and periodic acid-Schiff. We conclude that papillary carcinoma of the thyroid should be included in the differential diagnoses for a mucin-producing metastatic carcinoma.