Of 6,406 subjects, 3,353 subjects belonged to high-risk group who had smoked 20 pack years or more (39±15.9 pack years). Low-risk group included 3,053 subjects; 1,581 smokers who smoked less than 20 pack-years (13±4.7 pack years) and 1,472 non-smokers. All smokers had the mean smoking history of 33.3 pack years.
shows the characteristics of non-calcified nodules detected on LDCT scans. At CT, 35% (2,255 of 6,406) of screened subjects had at least one or more non-calcified nodules (n=4,037); 2,085 subjects had 3,783 solid nodules (mean, 1.8 nodules per subject) and 170 subjects 254 GGO nodules (mean, 1.5 nodules per subject).
Characteristics of non-calcified nodules detected by low-dose screening CT
shows the characteristics of lung cancers detected on LDCT scans. Twenty-three primary lung cancers were detected with an overall detection rate of 0.36% (23 of 6,406) on an individual basis and 0.57% (23 of 4,037) on a non-calcified nodule basis. The prevalence of lung cancer according to stratified subjects' ages was 0.36% (23 of 6,406) in those of ≥45 yr in age, 0.47% (20 of 4,254) in those of >50 yr, and 0.91% (11 of 1,215) in those of >60 yr.
Characteristics of detected lung cancers by low-dose screening CT
Adenocarcinoma was found in 12 patients (), squamous cell carcinoma in 6 (), bronchioloalveolar carcinoma in two, pleomorphic carcinoma in one and small cell carcinoma in two.
Fig. 1 A 48-yr-old man with adenocarcinoma. (A) Lung window of initial screening low-dose CT scan obtained at level of right upper lobar bronchus shows 10-mm-sized ground-glass opacity nodule (arrow) in right upper lobe. (B) Lung window of thin-section (2.5-mm (more ...)
Fig. 2 A 65-yr-old man with squamous cell carcinoma. (A) Lung window of initial screening low-dose CT (5-mm collimation) scan obtained at level of bronchus intermedius shows 5-mm-sized nodule (arrow) in bottom of anterior segment of right upper lobe. (B) Repeat (more ...)
On CT scans, 21 NSCLCs presented as a solid nodule in 14 patients and GGO in seven. The likelihood of lung cancer was higher in GGO nodules (7 of 254 GGO nodules, 3%) than in solid nodules (14/3,783, 0.4%) (p<0.01) (Fisher's exact test).
The pathologic stages of the 21 NSCLCs were as follows: T1 in 16 (76%) patients, T2 in 3 (14%), and T3 in 2 (10%); N0 in 13 (62%), N1 in 2 (10%), N2 in 3 (14%), and N3 in 3 (14%); and stage IA in 13 (62%), IIA in 1 (5%), IIIA in 4 (19%), IIIB in 1 (5%), and IV in 2 (10%).
Sixty-five percents (15 of 23) of lung cancers occurred in high-risk group and 35% (8 of 23) in low-risk group (p=0.215) (chi-square test). Of 13 stage IA NSCLCs, 8 (57% of 14 NSCLCs in high-risk group) were observed in high-risk group and 5 (71% of 7 NSCLCs in low-risk group) in low-risk group (p=0.656) (Fisher's exact test).
Of 23 lung cancers, 11 lung cancers were detected during initial screening and 12 during repeat study. In terms of repeat studies, 10 lung cancers were detected during the second follow-up study (mean 25.3 months) and 2 during the third follow-up study (mean 27.3 months). Of 9 NSCLCs detected at initial screening, three (33%) were stage IA cancers, whereas of 12 NSCLCs detected at repeat study, 10 (83%) were stage IA cancers, i.e., stage IA cancers were much more prevalent in the repeat study than in the initial study (p=0.032) (Fisher's exact test).
Of the 12 lung cancers for which the tumor doubling time was calculable, the average doubling time was 16±16.7 months (range; 1-49 months). Although this tumor doubling time was twice as long in low-risk (25±23.2, median; 24, range; 3-49) group as in high-risk (12±11.9 months, median; 5.0, range; 1-29) group, it was not statistically significant (p=0.368) (Mann-Whitney test).
Of 23 patients with lung cancer, lobectomy was performed in 15. Two patients underwent chemotherapy. Another patient underwent concurrent chemoradiation therapy. Five patients were discharged without any therapy because they declined treatment. Seventeen (74%) of 23 patients were still alive for 4 yr, 2 died, and 4 were lost during follow-up studies. Of the 17 living patients, 15 (65% [15/23]) were alive without tumor recurrence.