Clinicopathological, immunohistochemical, and mutational analyses of pulmonary enteric adenocarcinoma: usefulness of SATB2 and β-catenin immunostaining for differentiation from metastatic colorectal carcinoma

Pulmonary enteric adenocarcinoma (PEA) is a rare variant of pulmonary adenocarcinoma; it is sometimes difficult to discriminate between PEA and metastatic colorectal carcinoma (MCRC) because of their morphological and immunohistochemical resemblance. Here, we conducted clinicopathological, immunohistochemical, and mutational analyses of PEA with special focus on its differentiation from MCRC. We comparatively analyzed 8 surgically resected PEA tumors (7 patients) and 20 cases of MCRC. Patients were aged 43-77 years (average age, 64.1 years); 5 of 7 patients were men. Tumor sizes ranged from 1.5 to 11.5 cm (average size, 4.8 cm). The follow-up period was 1-65 months; 4 patients are alive without recurrence, 2 are alive with recurrence, and 1 patient died of idiopathic pulmonary fibrosis. Six of the tumors were pure PEA; one PEA tumor had a small mucinous adenocarcinoma component; another had a squamous cell carcinoma component. Immunohistochemically, the positive rates of PEA for each antibody were as follows: CK7, 88% (7/8); CK20, 88% (7/8); TTF-1, 13% (1/8); β-catenin, 0% (0/8, strong nuclear expression); and SATB2, 13% (1/8). The positive rates of MCRC for these antibodies were 10%, 95%, 5%, 55%, and 100%, respectively. Genetic analysis of KRAS, EGFR, and BRAF showed the G12V mutation in exon 2 of KRAS in 1 PEA. The present study's findings indicate that β-catenin and SATB2 are useful immunohistochemical markers for differentiating between PEA and MCRC.