Fig. 1.

Morphologic features of tumor sproutings. Tumor sprouting is present in the lower portion of the figure (blue box) separated from the main tumor in the upper portion (A) and a magnified view of blue-boxed area shows tumor sprouting. Tumor sprouting exhibits typical nuclear features of papillary thyroid carcinoma, but lacks evidence of lymphatic emboli such as an endothelialized tumor cluster or endothelialized lymphatic spaces (B). Another example of tumor sprouting. Tumor sprouting is easily found with cytokeratin 19 (CK19) or high molecular weight cytokeratin (HMW-CK) staining. Immunoreactivity with D2-40 is not observed (C, hematoxylin and eosin staining; D, CK19 staining; E, HMW-CK staining; F, D2-40 staining). (G) Another example of tumor sprouting (blue box). Tumor sproutings are observed around the main tumor mass. (H) High magnification view of tumor sprouting.