Papillary thyroid carcinoma with fibromatosis-like stroma: a report of two cases.

Two cases of an unusual morphologic variant of papillary thyroid carcinoma (PTC) are reported. Tumor cells had nuclear features of a typical papillary carcinoma, i.e., overlapping, pale to ground glass and/or grooved nuclei. Tumors were characterized by an extensive stromal component accounting for 40-60% of the tumor. It has been reported that PTC is associated with a variable degree of fibrosis, but the exuberant proliferation of fibroblasts resembling fibromatosis is rare. The histogenesis and clinicopathologic significance of PTC have not been fully clarified because of its rarity. It is possible that the malignant nature of these PTC lesions may be overlooked because attention is focused on the stromal component of the tumor. A diligent search for this variant of papillary carcinoma is important.