Adenocarcinoma arising within an intrapulmonary foregut duplication cyst: A case report

Foregut duplication cysts are congenital malformations that are usually associated with the gastrointestinal tract, but may be found in the lung. Here we report a case of a 74-year-old male who presented with a long-standing right lower lobe cystic lesion, which had recently developed a solid component which was hot on FDG-PET scanning. Examination of the resection specimen demonstrated a 62 mm adenocarcinoma arising from the wall of a foregut duplication cyst. The cyst lining was TTF1 negative, but NapsinA positive and morphologically had an enteric appearance despite negative staining for CDX2. The lining epithelium demonstrated progressive change from dysplasia, to adenocarcinoma in situ and thence invasive adenocarcinoma. The invasive component harboured both KRASG12D and PIK3CAQ546R mutations. Although rare, this case demonstrates that similarly to foregut duplications cysts arising elsewhere, adenocarcinoma may arise from an intrapulmonary foregut duplication cyst.