Nuclear protein content and Ki-67 immunoreactivity in nonneoplastic and neoplastic thyroid cells.

The nuclear DNA content in thyroid tumor cells has been shown to be closely related to the malignant potential of the neoplasm. Besides DNA, nuclear protein (NP) constitutes the major mass of the nucleus. The NP content may vary significantly in relation to the proliferative stage in growing as compared to growth-arrested cells. The increase in NP content associated with the transition from G0 to G1 occurs before the onset of DNA synthesis and may be used to assess growth activity. The nuclear DNA and NP contents were analyzed in 90 nonneoplastic lesions and 75 benign and 62 malignant thyroid tumors. All nonneoplastic specimens were euploid, and 1 of 90 was growth activated. In the group of benign tumors, 59 were euploid, and 16 were aneuploid. Among these there were 5 (9%) of 59 and 6 (38%) of 16 growth-activated specimens, respectively. In the group of malignant tumors 57 of 62 were classified as euploid, and in this group 12 (21%) showed growth activity according to the NP content. Five of 62 were aneuploid, and 3 (60%) of these 5 tumors were growth activated. Evaluation of the growth activity by means of monoclonal antibody Ki-67 was performed on a subgroup of 32 thyroid specimens, both nonneoplastic and neoplastic lesions. Ki-67 immunoreactivity was observed in 0-1.1% cells of 6 nonneoplastic lesions, in 0-3.1% cells of 14 benign cells and in 0.2-3.9% cells of 12 malignant thyroid tumors. Growth activity, as reflected by the NP/DNA ratio and Ki-67 immunoreactivity, appears to be low both in nonneoplastic thyroid lesions and thyroid tumors.