IDENTIFICATION OF A 35 KD TUMOR-ASSOCIATED AUTOANTIGEN IN PAPILLARY THYROID-CARCINOMA

Despite its tendency to metastasize and grow multifocally, papillary t hyroid carcinoma (PTC), the most common endocrine malignancy, usually displays an indolent clinical course. Although this behavior probably reflects the inherent low growth potential of PTC cells, it has been p ostulated that the striking inflammatory reaction often present in PTC represents the activation of a protective, tumor-induced immune respo nse. In a recent immunohistochemical study, we reported that immunoglo bulin (IgG) and complement (C3d, C4d and C5) are specifically deposite d in PTC tumor tissue. Endeavors were then made to isolate and identif y, tumor-associated antigens. Immunoprecipitation employing the serum and tumor tissue of PTC patients produced two bands by SDS-PAGE, at ap proximately 34.5 and 35 kD, which were not present in normal thyroid t issue. Three tryptic peptides of the 35 kD band were sequenced, identi fying it as a fragment of cytokeratin 1, a structural protein not norm ally expressed in the thyroid. The results indicate a tumor-specific a ntibody response against an aberrantly expressed protein in PTC.