## 5 Aldehydes Observed in the Exhaled Breath of Cancer Patients  
The large variations in the reported median concentrations of the exhaled aldehydes in Table 3 are common and can be attributed to differences in VOC capture technology, particularly with respect to the different solid-phase microextraction (SPME) materials that were used (e.g., Carboxen-polydimethylsiloxane (CAR/PDMS) or divinylbenzene-Carboxen-PDMS (DVB/CAR/ PDMS) vs. Tenax extraction). Differences in SPME fiber exposure times, differences in desorption protocols and analysis processes, differences in the patient populations examined, especially with respect to LC staging, and differences in the type of lung cancer studied (non-small cell lung cancer (NSCLC) vs. small cell lung cancer (SCLC)) also contributed to widening the concentration ranges noted for aldehyde biomarkers [101]. Biomarker quantification is further complicated by the nature of the VOC mixture. [PERSON] et al. compared the adsorptions of aldehydes to different fibers and found that aldehyde recovery by Carbowax/DVB fiber, for example, was lowered by a factor of seven when exposed to an aldehyde mixture compared to recovery on exposure to singular aldehydes [102]. Concentration variations in a population of samples can also be due to environmental effects. Exogenous sources of aldehydes include food consumption, tobacco use, and even inhaled aldehydes from aging building and floor materials in indoor environments [6,103], thus requiring careful control measurements.  
From Table 3, when plotting both the incidence of aldehyde detection in lung cancer patient breath and when the presence of a given aldehyde was determined to be a biomarker of lung cancer for that study, a qualitative assessment of LPO-derived aldehydes as indicators of lung cancer becomes evident (Figure 4). Saturated aldehydes are particularly well represented, and their presence is often significantly different in the EB of LC patients relative to healthy control (HC) subjects (Figure 4, red bars). In contrast, hydroxyldehydes and unsaturated aldehydes, which are derived from the same lipids and  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Year** & **Study b** & **Patients c** & **Stage d** & **Breath** & **Preconcentration** & **Analytical** & **Saturated Aldehydes** & **Unsaturated** \\
2020 & Munoz-Lucas [92] & 107 & NR & Bio-VOC & \
\begin{tabular}{c} carbon \\ tube \\ \end{tabular} & GC-MS &
\begin{tabular}{c} hexanal, heptanal, \\ nonanal \\ \end{tabular} \\
\begin{tabular}{c} \\ \end{tabular} \\
2022 & Larracy [98] & 100 & NR & — & Tenax TA & CRDS & hexanal \\  & & & & & & & \\  & & & & & & & \\
2022 & Soufi [99] & 5 & NR & Tedlar bag & naphthalene & GC-MS &
\begin{tabular}{c} pentanal, \\ nonanal \\ \end{tabular} \\
2022 & [PERSON] [100] & 60 & I–IV & Tedlar bag & \begin{tabular}{c} \\ \end{tabular} & \begin{tabular}{c} \\ \end{tabular} & \begin{tabular}{c} \\ \end{tabular} & \begin{tabular}{c} \\ \end{tabular} & \
\begin{tabular}{c} \\ \end{tabular} &
\begin{tabular}{c} \\ \end{tabular} \\ \hline \hline \end{tabular}  
random LPO processes, are not widely observed, possibly a result of their higher intrinsic reactivity resulting in lower, trace concentrations in exhaled breath. Below are study details for the aldehydes summarized in Table 3.