poorly differentiated thyroid cancer poorly differentiated thyroid cancer poorly differentiated thyroid carcinoma is malignant neoplasm of follicular cell origin showing intermediate histopathological patterns between differentiated and undifferentiated thyroid cancers. poorly differentiated thyroid carcinomaother namespdtcspecialtyoncology histopathology presence of small cells with round nuclei and scant cytoplasm with a diffuse solid pattern round or oval nests (insulae) or in trabeculae. solid growth and presence of microfollicles, some of which contain dense colloid. extrathyroidal extension and blood vessel invasion foci of necrosis, larger than 5 cm in greatest diameter at diagnosis epidemiology pdtc affects predominantly females about 55 years of age