DNA copy number loss and allelic imbalance at 2p16 in lung cancer associated with asbestos exposure

Abstract

Five to seven percent of lung tumours are estimated to occur because of occupational asbestos exposure. Using cDNA microarrays, we have earlier detected asbestos exposure-related genomic regions in lung cancer. The region at 2p was one of those that differed most between asbestos-exposed and non-exposed patients. Now, we evaluated genomic alterations at 2p22.1-p16.1 as a possible marker for asbestos exposure. Lung tumours from 205 patients with pulmonary asbestos fibre counts from 0 to 570 million fibres per gram of dry lung, were studied by fluorescence in situ hybridisation (FISH) for DNA copy number alterations (CNA). The prevalence of loss at 2p16, shown by three different FISH probes, was significantly increased in lung tumours of asbestos-exposed patients compared with non-exposed (P=0.05). In addition, a low copy number loss at 2p16 associated significantly with high-level asbestos exposure (P=0.02). Furthermore, 27 of the tumours were studied for allelic imbalances (AI) at 2p22.1-p16.1 using 14 microsatellite markers and also AI at 2p16 was related to asbestos exposure (P=0.003). Our results suggest that alterations at 2p16 combined with other markers could be useful in diagnosing asbestos-related lung cancer.

Figure 1

P arm of chromosome 2 showing microsatellite markers and bacterial artificial chromosome (BAC) clones used in fragment analyses and in fluorescent in situ hybridisation. Start and end base pairs are presented according to the University of California Santa Cruz (UCSC) genome browser.

Figure 2

(A) An example of a metaphase showing hybridisation signals of the RP11-703K23 probe in chromosome 2. (B) Lung tumour cells hybridised with the CEN2 centromeric probe (red) showing diploid to tetraploid cells and with the RP11-963J22 probe (green) showing gain of DNA at 2p21. (C) Lung tumour cells hybridised with the CEN2 centromeric probe (red) showing diploid to tetraploid cells and with the RP11-703K23 probe (green) showing loss at 2p16.

Figure 3

Significantly more allelic imbalances (AI) at 2p16 were found in asbestos-exposed patients' lung tumours compared with those of non-exposed (P=0.003, Fisher's exact test). ^aAC, adenocarcinoma; SCC, squamous cell carcinoma; SCLC, small cell lung cancer; LCLC, large cell lung carcinoma; ^bmillion g⁻¹ dry lung; ^cwhite, normal; light grey, no result; dark grey, allelic imbalance; MSI, microsatellite instability; bold when at least two markers showed AI.