multinodular goiter, or other differentiated carcinoma are usually present
bulky masses that typically grow rapidly beyond the thyroid capsule into adjacent neck structures
Any of the following pictures may be found in microscope
(1) large, pleomorphic giant cells;
(2) spindle cells with a sarcomatous appearance
(3) mixed spindle and giant-cell lesions
(4) small cells, resembling those seen in small-cell carcinomas
Foci of papillary or follicular differentiation may be present in some tumors, suggesting origin from a better differentiated carcinoma.