Mucinous carcinoma identified as lung metastasis from an early rectal cancer with submucosal invasion by immunohistochemical detection of villin.

We encountered a male patient aged 64 with pulmonary mucinous carcinoma in whom a diagnosis of pulmonary metastasis from early rectal cancer with submucosal invasion was made based on an immunohistochemical examination. A rectal cancer was detected together with a mass in the lung. The mass in the lung was consistent with mucinous adenocarcinoma, whereas the invasion of rectal cancer was confined to the submucosa; thus, distant metastases appeared unlikely. These lesions were assessed using immunohistochemical staining for cytokeratin and thyroid transcription factor-1, which failed to make a definite diagnosis. A further assessment was made by staining for villin. Both neoplasms were positive for this protein, demonstrating a common brush-border pattern. A lung metastasis from rectal cancer with submucosal invasion was diagnosed. Villin is considered useful for detecting primary neoplastic lesions based not only on its specificity but also on its staining pattern, which is different from that of other proteins.