Comparative Histopathologic Analysis of "radiogenic" and "sporadic" Papillary Thyroid Carcinoma: Patients Born Before and after the Chernobyl Accident.

Background: The issue of whether radiation-induced thyroid cancer is pathologically different from sporadic remains not fully answered. This study compared structural characteristics and invasive features of papillary thyroid carcinoma (PTC) in two age-matched groups: patients who were children (4 years old) at the time of the Chernobyl accident and who lived in three regions of Ukraine most contaminated by radioactive iodine I-131 (radiogenic cancer), and those who lived in the same regions but who were born after 1987 and were not exposed to I-131 (sporadic cancer). Further, the histopathologic features of PTC were analyzed in relation to age and individual I-131 thyroid dose. Methods: The study included 301 radiogenic and 194 sporadic PTCs. According to age at surgery, patients were subdivided into children (14 years old), adolescents (15-18 years old), and adults (19-28 years old). Statistical analyses included univariate tests and multivariable logistic regression within and across the age subgroups. Analyses of morphological features related to I-131 doses were conducted among exposed patients on categorical and continuous scales controlling for sex and age. Results: Among children, radiogenic PTC displayed a significantly higher frequency of tumors with a dominant solid growth pattern, intrathyroidal spread, extrathyroidal extension, lymphatic/vascular invasion, and distant metastases. Exposed adolescents more frequently displayed extrathyroidal extension, lymphatic/vascular invasion, and distant metastases. Exposed adults more frequently had intrathyroidal spread and extrathyroidal extension. The frequency of PTC with dominant papillary pattern and oxyphilic cell metaplasia was significantly lower in radiogenic compared to sporadic tumors for all age groups. Manifestations of tumor aggressiveness were most frequent in children compared to adolescents and adults regardless of etiology. Conclusions: Radiogenic PTC is less likely to demonstrate a dominant papillary growth pattern and more likely to display more aggressive tumor behavior than sporadic PTC. Histopathologic tumor aggressiveness declines with patient age in both radiogenic and sporadic cases.