Transformation to small cell carcinoma from adenocarcinoma.

(A) Adenocarcinoma, H&E; (B) small cell carcinoma, H&E; (C) small cell carcinoma, CK; (D) small cell carcinoma, CD56. Abbreviations: CD56, cluster of differentiation 56; CK, cytokeratin; H&E, hematoxylin and eosin.