Lung giant cell carcinoma is a specific type of lung carcinoma characteristically associated with a highly aggressive clinical behaviour. This tumour is usually defined as a malignant epithelial tumour with large nuclei, prominent nucleoli and abundant cytoplasm without the features of squamous cell, small cell or adenocarcinoma. Lung giant cell carcinoma, belonging to the group of pleomorphic carcinoma, occurs mainly in men who smoke heavily [1]. It is not routinely treated surgically, owing to the fact that it is metastatic at the time of diagnosis, but resection or radiation have been suggested to prolong survival time. We experienced a rare case of lung giant cell carcinoma accompanied by lung adenocarcinoma in a different lobe of the same patient. A 64-year-old man presented to our hospital with a seven-month history of shortness of breath. Smoking history was 40 cigarettes per day for 30 years. Physical examination and routine blood examination showed normal. Plasma levels of tumour markers were as follows: squamous cell carcinoma antigen, 4.1 ng/ml (normal range, 0 to 2.0 ng/ml); cytokeratin fragment, 2.62 ng/ml (normal range, 0 to 3.5 ng/ml); carcinoembryonic antigen, 70.4 ng/ml (normal range, 0 to 4.3 ng/ml); neuron specific enolase, 11.63 ng/ml (normal range, 0 to 17 ng/ml); CA19-9, 47.52 U/ml (normal range, 0 to 27 U/ml) and pro-gastrin-releasing peptide, 24.3 pg/ml (normal range, 0 to 46.0 pg/ml). Arterial blood gas analysis yielded the following: pH = 7.42, PO2 = 74 mm Hg, PCO2 = 40 mm Hg and oxygen saturation of 96%. The chest CT showed a ca. 2.5-cm soft-tissue density in the right upper lung field (Fig. 1A, ,B).B). Bronchoscopy was performed, revealing a neoplasm existing in the bronchial lumen of the left lingular segment, but normal mucosa in the right upper bronchi. By bronchoscopy, biopsy of the neoplasm revealed giant cell carcinoma in left lingular segment, with immunohistochemical characteristics positive for pan-cytokeratin and thyroid transcription factor 1 (TTF-1), weakly positive for vimentin and S-100 protein, and negative for desmin, chromogranin A, synaptophysin, P63 and CD68 (Fig. 2). Ultrasound-guided percutaneous lung biopsy of the node in the right upper lobe exhibited a poorly differentiated adenocarcinoma with immunohistochemical characteristics positive for cytokeratin 7 and TTF-1, and negative for cytokeratin 17 (Fig. 3). Metastatic disease was detected by brain CT, abdominal CT and bone scan, but the patient did not present with metastasis. Fig. 1 A) CT image showing nodular shadow in right upper lobe obtained from lung window. B) Nodular shadow from mediastinal window settings Fig. 2 Pathologic findings of the tumour obtained from biopsied neoplasm. The tumour was diagnosed as giant cell carcinoma. HE, magnification 100× Fig. 3 The tumour was diagnosed as adenocarcinoma. HE, magnification 100× At this time, the case was diagnosed as coexistent lung adenocarcinoma in the right upper lung field and giant cell carcinoma in the left lingular segment. Subsequently, the patient received radiotherapy in the bilateral upper lobes with a linear accelerator (6 MV). The field size of radiotherapy included the bilateral upper fields and mediastinal lymph node, and was treated with 2 Gy every day on a schedule of five fractions per week. The total dose was 64 Gy. At the same time as radiotherapy, cisplatin 50 mg (30 mg/m2) was administered weekly as a sensitizer of radiation. After radiotherapy, chest CT imaging revealed no change to the node in the right upper lobe, but the bronchial lumen of the left lingular segment became unobstructed by bronchoscopy (Fig. 4A, ,B).B). Subsequently, the patient underwent chemotherapy consisting of intravenous cisplatin 140 mg (75 mg/m2) on the 1st day and vinorelbine 40 mg (25 mg/m2) on the 1st and 8th days. The treatment was to be repeated every 21 days. After two chemotherapy cycles, the nodular shadow in the right upper lobe remained unchanged. Bronchoscopy was performed, and the bronchial lumen of the left lingular segment remained unobstructed. After ten months the patient died of respiratory failure because of obstructive pneumonia in the right upper lobe. Fig. 4 A) Neoplasm was discovered by bronchoscopy in the left lingular segment. B) The neoplasm of bronchial lumen in the left lingular segment disappeared after radiotherapy