Case 3. A smooth transition between well-differentiated papillary thyroid carcinoma, follicular variant (left side) and mammary analog secretory carcinoma component (right side) (a) (200 × magnification); TTF-1 immunostain is positive in well-differentiated papillary thyroid carcinoma (left side) and negative in mammary analog secretory carcinoma component (right side) (b) (200 × magnification). Papillary thyroid carcinoma is composed of colloid-filled follicles and tumor cells show pale eosinophilic cytoplasm, enlarged nuclei with irregular nuclear membranes, open chromatin and absent to inconspicuous nucleoli (c) (400 × magnification). The transition to the mammary analog secretory carcinoma phenotype is characterized by lack of colloid, denser eosinophilic cytoplasm, enlarged nuclei with open chromatin, and conspicuous to prominent nucleoli (d) (400 × magnification).