Primary pulmonary colloid adenocarcinoma: A case report of a rare subtype

Introduction and importance: Pulmonary colloid adenocarcinoma is an extremely rare subtype of lung adenocarcinoma. Owing to its rarity, the detailed clinical features of colloid adenocarcinoma remain largely unknown. This report describes a case of early-stage colloid adenocarcinoma that recurred soon after resection, including its radiological findings. Case presentation: During a routine checkup, a chest roentgenogram revealed an abnormal shadow in the right upper lung field of an asymptomatic 68-year-old man. Computed tomography (CT) showed a well-defined, low-attenuation nodule in the right upper lobe. Right upper lobectomy with mediastinal lymph node dissection was performed. The postoperative histopathological diagnosis indicated pulmonary colloid adenocarcinoma. The pathological stage was classified as T1bN0M0 (stage IA2). Follow-up CT 1 year after the resection revealed an enlarged supraclavicular lymph node and pulmonary nodule in the right lower lobe. Both lesions appeared as well-defined solitary hypoattenuated tumors with minimal enhancement on CT images. Excisional biopsies of both tumors were performed to obtain a definitive diagnosis. Both tumors consisted of abundant mucin in which some tumor cells were floating and were diagnosed as colloid adenocarcinoma recurrences. Clinical discussion: Although colloid adenocarcinoma is generally considered to have indolent clinical behavior, it can recur even in early-stage cases. Conclusion: Colloid adenocarcinoma is a distinct variant of lung adenocarcinoma, characterized by well-circumscribed mucinous lesions with alveolar wall destruction caused by mucin pools and scant tumor cells. The treatment strategy for colloid adenocarcinoma should follow the guidelines for primary lung cancer.