Distinguishing Pulmonary Enteric Adenocarcinoma from Metastatic Colorectal Adenocarcinoma

 

The routine histology of an enteric adenocarcinoma of the lung closely resembles that of a colorectal adenocarcinoma, with columnar cells showing an eosinophilic cytoplasm, a brush border and variable mucin production. It is important not to assume that the tumor is a metastasis on routine histology alone.

 

Most enteric adenocarcinomas will differ significantly from colorectal adenocarcinoma.

 

Immunoperoxidase Stain	Usual Phenotype for an Enteric Adenocarcinoma	Colorectal Adeno-carcinoma Phenotype
CK7	positive	negative
CK20	negative	positive
TTF-1	positive	negative
CDX2	negative	positive

 

However, cases of primary lung cancer have been reported that show the colorectal phenotype. Diagnosing an enteric lung carcinoma that shows the colorectal adenocarcinoma phenotype requires:

(1) a clinical history consistent with primay lung cancer

(2) absence of any evidence for a colorectal neoplasm after a careful evaluation, which may include colonoscopy and PET scanning

(3) absence of any evidence of a colorectal neoplasm on prolonged clinical followup.