Impact of autoimmune thyroiditis on the aggressiveness of papillary thyroid carcinoma and new cytological diagnostic criteria
Abstract
Background. Papillary thyroid carcinoma (PTC) coexisting with autoimmune thyroiditis (AIT) remains a controversial issue in thyroidology. The need to identify new cytomorphological criteria for malignancy in the context of chronic inflammation is critical to avoid false-positive diagnoses. The purpose was to investigate the influence of AIT on the aggressiveness of PTC and to identify cytomorphological markers that improve preoperative diagnostic accuracy. Materials and methods. A retrospective and prospective study was conducted on fine-needle aspiration biopsy specimens from 500 patients with thyroid nodules verified histologically. Cytomorphological and immunocytochemical analyses were performed to evaluate the expression of cytokeratins 7, 17, and thyroglobulin. To compare qualitative indicators (tumor aggression according to TNM classification, tumor and metastasis size, presence of vascular invasion, frequency of AIT in groups with and without metastasis), non-parametric χ2 test was used. Statistical comparison of metastasis sizes was determined using U-criterion. The difference was considered statistically significant at p < 0.05. Results. In 12 % of PTC cases with AIT, specific cytological complexes were identified, consisting of calcifications surrounded by epithelial cells; these were absent in benign thyroid nodules. Immunocytochemical analysis confirmed the epithelial and thyroid origin of these cells. It was statistically proven that patients with PTC and AIT had a lower incidence and a smaller size of metastasis (p < 0.05) compared to the PTC group without AIT. A significantly higher frequency of AIT was observed among patients without metastatic disease (p = 0.0056). Conclusions. In patients with autoimmune thyroiditis, metastasis from papillary carcinoma is less aggressive than in those without autoimmune thyroiditis, with a smaller size and frequency of metastases. Specific cytological complexes of psammoma bodies and thyroid cells have been found in papillary carcinoma biopsy specimens against the background of autoimmune thyroiditis, which can be markers for the cytological diagnosis of thyroid cancer with a specificity of 100 %.