Abstract
Background. Small cell carcinomas of unknown origin have been reported to occur in the hilum or mediastinal lymph nodes. Furthermore, there are a few reports describing the independent coexistence of pulmonary small cell cancer and pulmonary adenocarcinoma in a lung field. Case. A ground glass opacity (GGO) lesion was incidentally found in the right upper lobe on a chest CT image of a 67-year-old man. Positron emission tomography (PET) revealed accumulation in the hilar lymph nodes but distant metastasis was not seen, right upper lobectomy and lymph node dissection were performed. A pathological examination revealed that the GGO lesion of the right upper lobe was pulmonary adenocarcinoma, and small cell cancer was detected in the hilar lymph node. A thorough search of the whole range of the upper lobe was performed to detect macroscopic primary lesions. A primary small cell carcinoma of 2.5 mm in size was found in the upper lobe separate from the GGO lesion. The invasion of cancer cells into the lymphatic vessels was found around the small cell carcinoma. It was therefore diagnosed as a primary lesion of small cell carcinoma of the lung. Conclusion. When small cell carcinoma of unknown origin is detected in the hilum or mediastinal lymph nodes, a detailed examination may reveal primary cancer of the lung.
