## 2 Materials and Methods
### Analysis of the Exhaled Breath VOCs  
#### 2.3.1 Breath Sampling and Characterization  
The breath of seven patients with adenomatous colonic polyps was sampled with a ReCIVA(r) breath sampler (Owlstone Medical, Cambridge, UK). The breath-sampling kit consists of a mask and thermal desorption (TD) tubes ensuring reproducible collection of VOCs during real-time monitoring of the patient's breathing. A mask made in medical-grade silicone, including a low-resistance bacterial filter, was fixed to the device before each sampling. A medical air canister was then connected via a plastic pressure reducer, set to 15 L-min-1. The exhaled breath was captured in four TD tubes (Markes International, Llantrisant, UK; biomonitoring sorbent tubes) capable of retaining carbon compounds from C4 to C30. The alveolar fraction of the exhaled breath was selected through infrared carbon dioxide detection. The ReCIVA(r) breath sampler was connected to a laptop equipped with breath-sampling software (Owlstone Medical, Cambridge, UK), designed to ensure the accurate monitoring of breathing air pressure (partial pressure of carbon dioxide). All subjects fasted for at least 4 h before breath sampling.  
Sampling was always performed in the same room, aerated for 30 min before each procedure.  
The mask was securely adhered to the face and patients were instructed to breathe the air released by the medical air canister. After a 60-s ReCIVA(r) device washout with pure air (purity 99.99%; SOL Group, Monza, Italy), patient breath was collected for 10 min under PC-dedicated program control.  
Straight after sampling, the TD tubes were removed, covered with a plastic cap, and delivered to the chemistry department within 24 h for GC-MS analysis.  
Three TD tubes containing room air were sample-tested before commencement of the breath sampling on each sampling day to exclude environmental contaminations.  
VOCs collected in stainless steel TD tubes were desorbed with a thermal desorber (Unity-xr, Markes International), directly connected to the gas chromatograph with a heated transfer line. After heating each tube for 10 min at 220 C, the desorbed VOCs were directly interfect into the gas chromatograph injector at 200 C, operating in split mode (50% in and 50% out), utilizing helium as carrier gas, at a linear velocity of 0.5 cm\(\cdot\)s\({}^{-1}\). A gas chromatograph (Clarus 680, PerkinElmer, Waltham, MA, USA) coupled with a quadrupole mass spectrometer (Clarus SQ 8T, PerkinElmer) was used for separation and quantification of desorbed VOCs. A 60 m \(\times\) 0.25 mm i.d., 1.4 \(\mu\)m film thickness, capillary column Rtx(r)-VMS (Restek, Bellefonte, PA, USA) was utilized at 50 C for 5 min, then ramped 10 C-min\({}^{-1}\) to 160 C, 5 min at 160 C, ramped 10 C-min\({}^{-1}\) to 220 C, and 5 min at 220 C. The temperature of the transfer line was 280 C, whereas the ion source of quadrupole was 220 C. The MS was performed at 70 eV electron impact ionization energy, in full-scan mode (SCAN) with scan range of 40-250 amu. For compound identification and quantification SCAN monitoring mode was used. The Clarus SQ8 GC-MS software (PerkinElmer) was used for acquisition and elaboration of the data.  
To prevent memory effects, after each analysis, two empty TD tubes (without adsorbent phase) were analyzed to remove eventual residues of the previous sample from the thermal desorber and analysis apparatus.  
After each analysis, TD tubes were conditioned at 340 C for 3 h, as recommended by the producer, capped, sealed with parafilm, and stored at 8 C.