P1.03-041 Do Several Rounds of Negative Screening Low Dose CT Scans Influence the Risk to Develop Lung Cancer?

Abstract

The purpose of this study was to assess whether several years of negative screening low-dose computed tomography (LDCT) scans predict a subsequent lower risk of developing lung cancer. This would have implications for recommended intervals and duration of LDCT lung cancer screening. The cohort was an at-risk population who had previous negative screening LDCTs and had not been screened for at least 5 years. Between 2003 and 2009, 4782 individuals had been enrolled in a lung cancer screening study based on age and smoking alone. At this time, their risk was re-calculated using a multifactorial assessment model, and they were contacted in decreasing order of their re-calculated risk. An initial phone interview assessed interim history, general health, interim diagnosis of lung cancer or interim chest CT. Those participants without lung cancer or recent CT were invited for a single LDCT (40mA, 135kV, 1mm axial reconstructions). Subsequent investigation was recommended depending on the LDCT findings: negative, no new or growing nodules (no further recommendation), positive, low suspicion for malignancy (follow up CT in 3-6 months) or positive, high suspicion for malignancy (referral to the local lung cancer rapid diagnostic assessment program). To date, 361 individuals or family members have been contacted. Fifty-five individuals had passed away (20 from lung cancer), 24 were alive with lung cancer. 129 did not qualify for a LDCT scan (declined participation, or recent CT). A total of 153 have attended for LDCT, on average 7 years after their last LDCT. Ninety-one (59%) studies were reported as negative. Forty-five (29%) LDCTs were positive with low suspicion and a follow up scan was recommended; in 13 cases nodules had resolved on follow up imaging, the remaining 32 are awaiting surveillance LDCTs. Seventeen (11%) LDCTs were reported as positive with high suspicion; 11 of those have a subsequently biopsy proven lung cancer and 6 are currently undergoing further investigations or LDCT surveillance. All lung cancers diagnosed were either stage I or II. Of the 11 individuals with biopsy proven cancers, 7 had normal previous CTs, 4 had a pre-existing ground glass nodules in the tumor location on the most recent exam. The overall prevalence of lung cancer in this cohort is 15.2% (55/361) and it may increase. The detection rate of LDCT to date is 7.2% (11/153). Lung cancer risk remains high despite several negative annual screening LDCT scans. Continued screening beyond three years is recommended in high risk individuals.