Availability of Serum Levels of Carbohydrate Antigen 19-9 (CA19-9) as a Surrogate Tumor Marker for Papillary Thyroid Carcinoma

Introduction: Thyroglobulin (Tg) is a very sensitive and specific marker in patients who have undergone total thyroidectomy for papillary thyroid carcinoma (PTC). However, the presence of a Tg antibody (TgAb) interferes with Tg immunometric assays, making Tg levels unreliable indicators. There are currently no other tumor markers to monitor in patients with PTC whose serum is TgAb-positive. Thus, we investigated whether carbohydrate antigen 19-9 (CA19-9) can be used as a tumor marker for PTC. Methods: We retrospectively analyzed 196 consecutive patients with PTC (maximum diameter ≥ 2 cm). The serum CA19-9 and Tg values of each patient were obtained before and 0.5-1 month postsurgery. Immunohistochemical staining for PTC was performed using an antibody against CA19-9. Results: High pre-surgery serum levels of CA19-9 were observed in 6.1% of the patients. Postsurgery, serum CA19-9 levels in all 196 patients decreased considerably and were within the normal range. CA19-9 expression was detected in 28 of 62 PTCs (45.2%) and was detected at various degrees and ranges in conventional PTC histology. Conclusions: Although further studies with longer follow-ups are necessary, serum CA19-9 levels may serve as a surrogate tumor marker for PTC in place of serum Tg levels sin some patients.