Growth rate of small lung cancers detected on mass CT screening

CT has recently been used in mass screening for lung cancer. Small cancers have been identified but the growth characteristics of these lesions are no t fully understood. We identified 82 primary cancers in our 3-year mass CT screening programme, of which 61 were examined in the present study. The vo lume doubling time (VDT) was calculated based on the exponential model usin g successive annual CT images or follow-up CT images. All cases were also e xamined in the hospital by high resolution CT (HRCT). Lesions were divided into three types based on HRCT characteristics: type G (n=19), ground glass opacity (GGO); type GS (n=19), focal GGO with a solid central component; a nd type S (n=23), solid nodule. 18 (95%) lesions of type G, 18 (95%) of typ e GS and 7 (30%) of type S were invisible on conventional chest radiographs . The mean size of the tumour was 10 mm, 11 mm and 16 mm for type G, type G S and type S, respectively. Most tumours (80%) were adenocarcinomas; 78% of these were GGO (type G and GS). Mean VDT values were 813 days, 457 days an d 149 days for type G, type GS and type S, respectively; these are signific antly different from each other (p<0.05). Our results show that annual mass screening CT for 3 successive years resulted in the identification of a la rge number of slowly growing adenocarcinomas that were not visible on chest radiographs.