A case of concurrent follicular lymphoma and lung cancer requiring differentiation from lymph node metastasis.

Lung cancer complicated by follicular lymphoma has rarely been reported in the literature. A 69-year-old male with an abnormal shadow on a chest radiograph was referred to our hospital. A mass in the right lung was seen on chest computed tomography (CT). Positron emission tomography-CT showed fluorodeoxyglucose accumulation in the esophagus and multiple intra-abdominal lymph nodes, in addition to the right lung lesion. The lung lesion was diagnosed as a pulmonary adenocarcinoma after biopsy. Upper and lower gastrointestinal endoscopies did not reveal the presence of a tumor. Open lymph node biopsy was performed to determine the course of treatment, leading to a diagnosis of follicular lymphoma. The patient finally underwent radical resection for lung cancer; the follicular lymphoma was judged to be low-grade and was followed up. When complications involving other organs are detected during systemic examination of a patient with lung cancer, it is necessary to distinguish between metastasis to other organs and complications of other malignant diseases, as this will greatly influence the treatment strategy.