CA125 and thyroglobulin staining in papillary carcinomas of thyroid and ovarian origin is not completely specific for site of origin

Aims: A 70-year-old woman presented with metastatic psammoma body-rich papi llary carcinoma in a supraclavicular lymph node. No primary site was eviden t. The tumour showed strong staining for CA125 and weak staining for thyrog lobulin. Prompted by this case we aimed to assess the reliability of immuno staining for CA125 and thyroglobulin in making the distinction between thyr oid and ovarian papillary carcinoma. Methods and results: Nine papillary carcinomas of the thyroid and 17 serous papillary carcinomas of the ovary were stained for CA125 and thyroglobulin , as well as CAM 5.2, LP 34, carcinoembryonic antigen (CEA), S100 and diast ase/periodic acid-Schiff. Nine of nine thyroid carcinomas stained for thyro globulin; in addition CA125 was positive in four of nine. Normal surroundin g thyroid also showed some reaction. Seventeen of 17 ovarian serous carcino mas were positive for CA125; in addition one case showed moderately strong staining for thyroglobulin. Mucin stains were positive in 14/17 ovarian ser ous carcinomas, but negative in all thyroid carcinomas. The other antibodie s assessed showed no useful differences in staining frequency. Conclusion: Many cases of papillary carcinoma of the thyroid show CA125 sta ining, and this feature therefore has little positive predictive value for an ovarian origin. Occasional cases of ovarian papillary carcinoma may show staining for thyroglobulin, and this result should therefore be interprete d cautiously.