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Primary pulmonary adenocarcinoma with enteric differentiation resembling  metastatic colorectal carcinoma: A report of the second case negative for cytokeratin 7

Res. Pract (2010), doi:10.1016/j.prp.2010.07.005
abstract
We report the case of a 51-year-oldwomanwith pulmonary adenocarcinomawith enteric differentiation
(PAED) that is indistinguishable frommetastatic colorectal carcinoma by immunohistochemistry as well
as histology. A chest computed tomography scan revealed a 1 cm nodule in the right upper lobe and a
3 cmmass in the left lower lobe. Initial examination showed no evidence of any other tumor. She under-
went partial resection of the right upper lobe and left lower lobectomy. Histopathological examination
revealed that both tumors were composed of medium to large complex glands with central necrosis.
The tumor cells were cuboidal to tall columnar with eosinophilc cytoplasm, oval nuclei, and brush-
border. Immunohistochemical study yielded the following results: tumor cells were diffusely positive
for cytokeratin (CK) 20 and CDX-2, and negative for CK7, thyroid transcription factor-1, and Napsin A.
MUC2 was partially observed, while MUC5AC was not detected. These findings were strongly indicative
of metastatic colorectal carcinoma. However, no primary colorectal cancer was detected in any clinical
examination, including fluorine 18-labeled fluorodeoxyglucose-positron emission tomography scan and
video capsule endoscopy, and she has not presented with any characteristic symptoms at any follow-up
to date, approximately 4 years after operation. From all features, the final diagnosis was primary PAED,
suggestive ofmultifocal primary lung cancer. So far, only 1 case of CK7-negative PAED has been reported.
This is the second case of primary PAED resembling metastatic colorectal cancer morphologically and
immunohistologically.