Stromal elastosis in papillary thyroid carcinomas.

Stromal elastosis, defined as dense aggregations of elastic fibers, is found in some neoplastic tissues especially in malignant tumors of the breast and lung. Although also found in thyroid tissue, stromal elastosis in thyroid neoplasms have received little attention. To clarify the histopathological significance of stromal elastosis in the thyroid, we examined neoplastic (n = 223) and hyperplastic (n = 82) thyroid tissues in conjunction with cancer tissues (n = 193) of various other organs. Stromal elastosis was observed as deposits of pale homogeneous material in hematoxylin and eosin stain, and distinctively highlighted by elastic-van Gieson's stain. On immunohistochemical examination, elastin and tropoelastin were confirmed in these deposits. Stromal elastosis was found in 66% of papillary thyroid carcinomas (PTCs), although it was not identified in other histological types of thyroid neoplasms. In PTCs, deposits of elastic fibers varied in size and shape, and were more frequently distributed in the periphery of the tumor tissue. The histological subtypes of PTC varied in prevalence of elastosis with the follicular variant's (9%) prevalence being significantly lower than that of the classical type (72%). The frequency of stromal elastosis in PTCs was very similar to the frequencies in breast and lung adenocarcinomas, and higher than the frequencies in carcinomas of other organs. In conclusion, our results suggest that stromal elastosis is a characteristic histological finding of PTCs, presumably associated with their growth pattern and/or histological architecture. It is, therefore, reasonable to propose that stromal elastosis is an ancillary feature in the histopathological diagnosis of PTCs.