Background: Owing to the advent of refined chest computed tomography (CT) images with higher resolution and CT screening programs, more faint and smaller lung cancers are being discovered. These include small-sized lung cancers such as those with a subcentimeter diameter, which had never been picked up on the routine chest roentgenogram films. However their clinicopathological characteristics with special reference to the proper surgical mode are not fully described so far.
Methods: During a 10-year period from 1991 through 2000 a total of 1,769 lung tumors were resected at the National Cancer Center Hospital, Tokyo. According to the pathology files of these patients, 51 patients had a primary tumor with the diameter of 1 cm or less. Three tumors arising in the bronchial lumina of hilum with a squamous cell carcinoma histology were excluded and the remaining 48 tumors of peripheral origin were studied. The clinicopathological features were analyzed according to three types of appearance on high-resolution CT: non-solid ground glass opacity (GGO) type (n = 19); part-solid GGO type (n = 9); and solid type (n = 20). Non-solid GGO is made up of homogeneous moderate increased density on CT, which cannot obscure the bronchovascular structure, whereas partly solid GGO contains a mere solid part but did not exceed 50% of the whole area (n = 9). All other lesions were considered solid type.
Results: For the three types of lesions, the distribution of age and sex was similar with the average age of 61 years and an almost even distribution of male/female patients. Although 6 patients had symptoms, the symptoms were not associated with the nodule itself. Twenty-six patients (54%) were screen-detected (16 chest roentgenogram films and 10 CT scans) and the others were detected by incidentally taken chest roentgenogram film or CT for other reasons than nodules detected. Two squamous carcinomas were positive for sputum cytology. Preoperative cytologic/histologic diagnosis was given in 14 patients (29%). The histologic type of GGO lesion was bronchioloalveolar carcinoma in all 28 cases. In solid lesions, besides 16 adenocarcinomas 2 cases of squamous cell carcinoma, 1 case each of small cell carcinoma and carcinoid tumor was seen. Lymph node involvement was seen only in 3 patients with solid lesions (N1 in 2 patients, N2 in 1 patient). As for operative mode, the limited resection was performed for 15 GGO lesions (54%) and 4 solid lesions (20%). Tumor recurrence was seen in 2 patients with solid lesions-1 in bone and the other in locoregional lymph node, and the former died of disease.
Conclusions: Among subcentimeter lung cancers, GGO lesions (both non-solid and part-solid) constitute true early lung cancers. Since they have minimal or no invasive growth, limited resection for cure is justified. Conversely the solid lesion had significant invasive features such as lymph node metastasis. Lobectomy should remain as the standard mode of surgery despite such small size.