## 3 Results
### Age, Gender, and Ethnicity Influence the Expression of the ABCB1 Gene  
The next stage of the study was to analyze the demographic characteristics of patients with non-small-cell lung cancer and how they affected the expression of the \(ABCB1\) gene. The levels of \(ABCB1\) expression in cancer tissues, regardless of the age range, were characterized by similar values that significantly differed from the level of expression in healthy tissue. Moreover, in squamous-cell lung cancer, the lowest level of expression was found in the tumor tissues of patients aged 21-40, and it was significantly lower than the levels in the groups aged 61-80 (\(p<0.001\)) and 81-100 years (\(p=0.0106\), Figure 5B). This parameter also differed significantly between the 41-60 and 61-80 age groups (\(p=0.0136\)). In the glandular type of cancer, similar dependencies could be observed; however, the differences may have been a consequence of the different sample sizes in the analyzed subgroups (Figure 5A). Lower expression of the \(ABCB1\) gene was specific not only to younger patients with lung cancer but also to women and people of African American and Asian descent; however, this only applied to the LUAD subtype. As shown in Figure 5C, the median expression levels of the tested gene in neoplastic tissues differed only slightly between women and men; nevertheless, the expression appeared to be significantly higher in male adenocarcinoma cells (\(p=0.0391\), Figure 5C). The highest expression in lung adenocarcinoma tissues was observed in representatives of the Caucasian population (\(p=0.0294\)), and the lowest expression was observed in the Asian population, although compared to the others, this ethnic group was represented by only a few individuals in the analysis (Figure 5E). Among patients with squamous-cell lung cancer, the median levels of P-gp gene expression in cancerous tissues were similar regardless of sex in all ethnic groups, without significant differences (Figure 5D,F). Figure 4: Comparison of \(ABCB1\) expression between normal tissues and cancer tissues in relation to smoking status in (**A**) LUAD and (**B**) LUSC (* \(p<0.05\); UALCAN). The Higher Stage of Cancer May Be Associated with a Decrease in the Amount of the ABCB1 Gene Transcript  
The next part of the analysis of _ABCB1_ gene expression in NSCLC was aimed at determining its potential impact on the clinicopathological features of the cancer. By analyzing the relationship between the expression of the _ABCB1_ gene and the stage of cancer in adenocarcinoma, it was found that between stage I and stage III there was a statistically significant decrease in the expression of the gene for P-gp (\(p\) = 0.0387), while in patients with the most advanced stage of cancer, the amount of mRNA in the tumor  
Figure 5: Comparison of _ABCB1_ expression between normal tissues and cancer tissues (LUAD (**A**,**C**,**E**) and LUSC (**B**,**D**,**F**)), depending on age (**A**,**B**), gender (**C**,**D**), and race (**E**,**F**) (\(\text{\textbullet}\)\(p\)\(<\) 0.05, \(\text{\textbullet}\)\(p\)\(<\) 0.001; UALCAN). cells increases again (\(p\) = 0.0484, Figure 6A). Similar observations applied to squamous-cell carcinoma (\(p\) = 0.0006), although in the highest stage of this type of cancer, a further decrease in \(ABCB1\) expression was seen (\(p\) = 0.0062, Figure 6B). However, this may have been due to the small size of this subgroup. This may also indicate a connection between \(ABCB1\) amplifications and the terminal stage of lung cancer as well as patient survival. Figure 6: Comparison of \(ABCB1\) expression between normal tissues and cancer tissues (LUAD (**A**,**C**,**E**) and LUSC (**B**,**D**,**F**)), depending on lung cancer staging (**A**,**B**), metastatic lymph node status (**C**,**D**), and _TP53_ mutation status (**E**,**F**) (* \(p\) < 0.05; ** \(p\) < 0.01; *** \(p\) < 0.001; UALCAN).