Peculiar nuclear clearing composed of microfilaments in papillary carcinoma of the thyroid

Background. Papillary carcinoma of the thyroid frequently occurs in young women. Four cases of papillary carcinoma were found in women in their 20s, and the disease was characterized by unusual morphologic and clinical features. Methods. Four cases were analyzed clinically, grossly, microscopically, ultrastructurally, and immuno‐histochemically and compared with control cases of papillary carcinoma. Results. The tumors histologically showed various appearances with trabecular, solid cribriform, follicular, and papillary patterns. A striking finding was that stratified cancer cell nests with prominent nuclear clearings were scattered in the tumors. Ultrastructurally, the nuclear clearings were composed of fine thread‐like fibrils, and they were bound unselectively to various antibodies against hormones and intermediate filaments. The four patients also had common clinicopathologic features as follows: they were all women in their 20s and their preop‐erative serum thyroglobulin levels were all normal despite the large size of their thyroid tumors. The tumors were grossly well encapsulated, and there was no lymph node metastasis, except in one patient who had only one positive node. Conclusions. The peculiar nuclear features were distinct from intranuclear cytoplasmic inclusions or ground‐glass nuclei, and these have not been reported previously to the authors' knowledge in conventional thyroid neoplasms. These tumors might represent another subtype of papillary thyroid carcinoma.