## 4 Discussion  
Generally, the coenzymes NADH and FAD are dominant in the autofluorescence signals in cells and tissues. When lung cancer develops, the redox equilibria in tissues changes with different  
Figure 4: Scatterplot of the average ratio of (**a**) \(I_{\mathrm{NADH}}/I_{\mathrm{FAD}}\) and (**b**) \(I_{630\,\mathrm{nm}}/I_{590\,\mathrm{nm}}\) for the normal (solid square) tissues and cancerous tissues (hollow triangle) from the ten lung cancer patients. metabolic conditions [43], which can be monitored through the autofluorescence spectra. In this study, we found the majority of patients presented lower \(I_{\mathrm{NADH}}/I_{\mathrm{FAD}}\) values in tumor tissues, which means a lower concentration of NADH and a higher concentration of FAD were in cancerous tissues compared with normal lung tissues. Our results agreed with some recent reports that the amount of FAD in tissues increased in the neoplasia, such as colonic cancer [44], cervical cancer [45], and human papillomavirus immortalized epithelial cells [46]. It implied the cellular metabolism changed due to the rapid tumor cell division. The alteration of NADH and FAD in cancerous tissues can serve as markers of metabolic activity and the cellular microenvironment [47]. Particular attention was given to the endogenous porphyrin derivatives for the detection of cancer in recent decades. [PERSON] et al. observed enhanced fluorescence of protoporphyrin (PpDX) and uroporphyrin III in colon tumor tissues and involved lymph node tissues [17]. [PERSON] et al. observed enhanced fluorescence bands (one around 590 nm and another around 630 nm) in blood samples for several different types of cancers, such as gastric cancer, breast cancer, and [PERSON]'s lymphoma [40]. [PERSON] et al. found elevated porphyrin fluorescence in the blood components of cervical cancer patients [36]. It indicates that porphyrins accumulate more in tumor parts. The knowledge about the mechanisms of precursor 5-ALA lead to PpIX accumulation was demonstrated in many tumor diseases [48; 49; 50]. Our results showed that for the majority of the patients (80.0%), \(I_{\mathrm{630\;nm}}/I_{\mathrm{590\;nm}}\) of each individual patient's tumor sample was higher than that of normal sample. This further supported that the tumor metabolic alterations cause the accumulation of products of porphyrins. [PERSON] et al. found that the ratio of \(I_{\mathrm{630\;nm}}/I_{\mathrm{585\;nm}}\) in blood or urine samples was about one for normal controls and 2-3 for advanced cervical cancer patients [51]. Similar findings were also reported in blood samples of gastric cancer and breast cancer patients [40]. However, for lung tissue samples in our study, the porphyrins were present in fairly low amounts (Figure 3). It should be noted that \(I_{\mathrm{630\;nm}}/I_{\mathrm{590\;nm}}\) between normal and cancerous tissue samples showed considerable overlap among the patients as shown in Figure 4. Similar results can also be found for \(I_{\mathrm{NADH}}/I_{\mathrm{FAD}}\) values. This inter-patient variation was disadvantageous to analyze the averaged spectra data of patients. Therefore, the signature of spectra for lung tissues may be applicable for the assessment of per individual patient, instead of comparing one patient data with average values. Several studies reported that high NLR value is always associated with inflammation, poor survival and a higher risk of distant metastasis [52; 53]. The patients could be separated into two groups according to their NLR values. One group (numbers 1-4, 9-10) was of low NLR values (\(\leq\)3) and the other group (numbers 5-8) of high NLR values (\(>\)5). The low NLR group presented similar results of spectra with small fluctuation, while the high NLR group showed fairly large heterogeneity for each patient. Especially, the spectra of patient 8 with a high NLR value had different results both in \(I_{\mathrm{NADH}}/I_{\mathrm{FAD}}\) and \(I_{\mathrm{630\;nm}}/I_{\mathrm{590\;nm}}\) values than the remaining patients.