Short- and long-term lung cancer risk associated with noncalcified nodules observed on low-dose CT

Abstract

Chemoprevention is an important potential tool in reducing lung cancer incidence. Noncalcified nodules (NCN) observed on low-dose computed tomography (LDCT) have been proposed as intermediate endpoints in chemoprevention trials, but whether NCNs represent cancer precursors is unclear. We analyzed data from subjects in the LDCT arm of the National Lung Screening Trial (NLST) to examine short- and long-term lung cancer risks associated with NCNs and to elucidate whether some NCNs may be cancer precursors. NLST subjects received a baseline and two additional LDCT screens and were followed for a median of 6.5 years. We examined lung cancer incidence over three distinct periods from baseline-0-23 months (short-term), 24-59 months (medium-term), and 60-84 months (long-term)-in relation to baseline NCN characteristics. Spatially, lung cancer incidence was analyzed at the person, lung, and lobe levels relative to NCN location. A total of 26,272 subjects received the baseline LDCT screen, with 468, 413, and 190 lung cancers observed in the three periods. The presence of an NCN gave significantly elevated long-term lung cancer risk ratios (RR) of 1.8, 2.4, and 3.5 at the person, lung, and lobe levels; corresponding short-term RRs were 10.3, 16.8, and 38.0. Ground-glass attenuation was positively associated with long-term lung cancer risk but inversely associated with short-term risk; NCN size was positively associated with short-term risk but not significantly associated with long-term risk. That NCNs convey significantly elevated excess long-term of lung cancer lends evidence to the hypothesis that some NCNs may be cancer precursors.

Figure 1. Schematic of per-person, per-lung and per-lobe analyses

For a hypothetical sample subject with a NCN in the right upper lobe and a subsequent cancer diagnosed in the right lower lobe, both NCN status and lung cancer status (Pos=positive, Neg=negative) at each spatial level of analysis are displayed. The lingula is counted as a lobe.